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HELDIANA

Botany

NEW SERIES, NO. 43

El Nino in Peru:

Biology and Culture Over 10,000 Years

Jonathan Haas and Michael O. Dillon, Editors

July 31, 2003
Publication 1524

PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY

EL NINO IN PERU:

BIOLOGY AND CULTURE

OVER 10,000 YEARS

Papers from the VIII Annual

A. WATSON ARMOUR III SPRING SYMPOSIUM
MAY 28-29, 1 999 CHICAGO

FIELDIANA

Botany

NEW SERIES, NO 43 NATURAL \ F5TC&Y SURVEY

AUG 8 2003
LIB&AIN

El Nino in Peru:

Biology and Culture Over 10,000 Years

Jonathan Haas and Michael O. Dillon, Editors

Field Museum of Natural History
1400 South Lake Shore Drive
Chicago, Illinois 60605-2496
U.S. A.

Published July 31, 2003
Publication 1524

PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY

2003 Field Museum of Natural History

ISSN 0015-0746
PRINTED IN THE UNITED STATES OF AMERICA

CONTENTS

Contributors vii

Introduction ix

1 The Lomas Formations of Coastal Peru: Composition and
Biogeographic History 1

Michael O. Dillon, Miyuki Nakazawa, and Segundo Leiva Gonzdles

2 Response of a Land Snail Species (Bostryx conspersus) in the
Peruvian Central Coast Lomas Ecosystem to the 1982-1983 and
1997-1998 El Nino Events 10

Rina Ramirez, Saida Cordova, Katia Caro, and Janine Dudrez

3 Debris-Flow Deposits and El Nino Impacts Along the Hyperarid
Southern Peru Coast 24

Luc Ortlieb and Gabriel Vargas

4 Paleoenvironment at Almejas: Early Exploitation of Estuarine

Fauna on the North Coast of Peru 52

Shelia Pozorski and Thomas Pozorski

5 The Impact of the El Nino Phenomenon on Prehistoric Chimu
Irrigation Systems of the Peruvian Coast 7 1

Thomas Pozorski and Shelia Pozorski

6 El Nino, Early Peruvian Civilizations, and Human Agency:

Some Thoughts from the Lurin Valley 90

Richard L. Burger

Contributors

Editors

Jonathan Haas

Anthropology Department

Field Museum

1400 So. Lake Shore Drive

Chicago, Illinois 60605-2496

U.S.A.

(jhaas@fmnh.org)

Michael O. Dillon

Botany Department

Field Museum

1400 So. Lake Shore Drive

Chicago, Illinois 60605-2496

U.S.A.

(dillon @ sacha.org)

Contributors

Richard L. Burger

Peabody Museum of Natural History

Yale University

170 Whitney Avenue

New Haven, Connecticut 06520

U.S.A.

(Richard.Burger@yale.edu)

Katia Caro

Museo de Historia Natural

Universidad Nacional Mayor de San Marcos

Apartado 14-0434

Lima- 14, Peru

Saida Cordova

Museo de Historia Natural

Universidad Nacional Mayor de San Marcos

Apartado 14-0434

Lima- 14, Peru

Janine Duarez

Museo de Historia Natural

Universidad Nacional Mayor de San Marcos

Apartado 14-0434

Lima- 14, Peru

Segundo Leiva Gonzales

Museo de Historia Natural
Universidad Privada Antenor Orrego
Trujillo, Peru

Miyuki Nakazawa

Department of Biology
Kyushu University
6-10-1 Hakozaki, Higashi-ku
Fukuoka 812-8581, Japan
(chn52010@par.odn.ne.jp)

Luc Ortlieb

Institut de Recherche pour le Developpement

UR Paleotropique

32 Avenue Henri-Varagnat

F-93143 Bondy-Cedex, France

(Luc.Ortlieb@bondy.ird.fr)

Shelia Pozorski

Department of Psychology and Anthropology

University of Texas-Pan American

Edinburgh, Texas 78539

U.S.A.

(spozorski@panam.edu)

Thomas Pozorski

Department of Psychology and Anthropology

University of Texas-Pan American

Edinburgh, Texas 78539

U.S.A.

(tpozorski @ panam.edu)

Rina Ramirez

Museo de Historia Natural

Universidad Nacional Mayor de San Marcos

Apartado 14-0434

Lima- 14, Peru

(rinarm@pucrs.br)

Gabriel Vargas

Institut de Recherche pour le Developpement

UR Paleotropique

32 Avenue Henri-Varagnat

F-93143 Bondy-Cedex, France

(Gabriel.Vargas@bondy.ird.fr)

Departamento de Geologia
Universidad de Chile
Plaza Ercilla 803
Santiago, Chile
(gvargas@ing.uchile.cl)

Title-page illustration: Moche fineline painting from northern Peru
showing a naturalistic figure in an animated reed boat. The draw-
ing is by Donna McClelland and is reproduced from Moche Fine-
line Painting: Its Evolution and Its Artists (UCLA Fowler Museum
of Cultural History, 1 999) courtesy of the artist, the authors, Chris-
topher Donnan and Donna McClelland, and the publisher. The ves-
sel from which the drawing was made is in the collections of the
Art Institute of Chicago.

Introduction

On May 28-29, 1999, a group of sixteen scientists met at the Field
Museum in conjunction with the VIII Annual A. Watson Armour
III Spring Symposium to discuss the impacts of the El Nino phe-
nomenon on the biology and cultural history of coastal Peru over
the last 10,000 years. The meeting brought together anthropolo-
gists, archaeologists, and biologists with a shared interest in the
effects of this potent global weather disturbance. The one-day
workshop and subsequent symposium presented research results
documenting the impact of this phenomenon from a wide range of
perspectives. The papers published here represent the results of
research from these various fields and differing points of view.
The impact of El Nino on terrestrial and marine ecosystems has
been well documented over the last 20 years, but the interpretation
of these results remains controversial. The common thread linking
most of these efforts is an attempt to date the onset of the El Nino
phenomenon using various types of proxy data. Estimates range
from a few thousand to tens of thousands of years. Whatever its
age, it is obvious that El Nino had and continues to have a pro-
found impact on the coastal environments of Peru, and more gen-
erally of western South America.

Michael O. Dillon

The Lomas Formations of Coastal Peru:
Composition and Biogeographic History

Michael O. Dillon, Miyuki Nakazawa, and Segundo Leiva Gonzdles

For nearly 3,500 km along the western coast of
South America (5-30S latitude), the Atacama
and Peruvian deserts form a continuous hyper-
arid belt, broken only by occasional river val-
leys from the Andean Cordillera. Native vege-
tation of the deserts is largely restricted to a
series of fog-dependent communities termed lo-
mas formations, meaning small mountains. This
chapter provides a backdrop for the subsequent
discussions in this volume of human occupation
in coastal Peru over the last 10,000 years. This
requires a synthesis of the present-day coastal
vegetation, analysis of the origins of the mod-
ern flora, and reconstruction of past climates,
including the onset of El Nino conditions, using
proxy data from a variety of sources. Paleocli-
matic data suggest that arid conditions existed
along the coast prior to 100,000 years ago, well
before the arrival of the first humans in western
South America. Distributional patterns and re-
lationships within specific members of the flora
are discussed to help explain current conditions.
Specifically, we have examined relationships in
the flowering plant genus Nolana (Solanaceae),
a group of over 80 species distributed predom-
inantly in the lomas formations of Peru and
Chile. The reconstructed phylogeny of Nolana
provides a framework for examining the coastal
lomas formations and the processes important
in their evolution, including the effects of gla-
cial cycles, sea level changes, and the historical
development of the El Nino-Southern Oscilla-
tion weather phenomenon.

Introduction

Much of the western coast of South America
(5-30S latitude) is occupied by deserts, form-
ing a continuous belt that extends for more than
3,500 km along the western escarpment of the
Andean Cordillera, from northern Peru to north-
ernmost Chile. The climate and geomorphology
of this region have been discussed in detail
elsewhere (Dillon 1997; Ferreyra 1953; Rundel
et al. 1991), and only a brief sketch is provided
here for discussion purposes. The Peruvian de-
sert is a narrow coastal band at the base of the
Andean Cordillera that extends nearly 2,000 km
in length but is only 50-100 km wide. The de-
sert is interrupted only by occasional rivers that
reach the coast, and their borders support ripar-
ian vegetation common to the inland river val-
leys. The factors responsible for the develop-
ment of the hyperarid conditions include isola-
tion from eastern weather patterns by the An-
dean Cordillera, and temperature homogeneity
resulting from the influence of cool sea-surface
temperatures associated with the south-to-north
flow of the Humboldt (Peruvian) Current. This,
combined with a positionally stable subtropical
anticyclone, results in a mild, uniform coastal
climate with the regular formation of thick fogs
below 1 000 m elevation from September to De-
cember.

Where the coastal topography is low and flat,
this stratus layer dissipates inward with little bi-
ological impact (Figs. 1 and 2A), but where iso-
lated mountains or steep coastal slopes intercept

M. O. Dillon et al

o vegetation

Tillandsia spp. 4-800

fv" woody plants

o:6-. o: ./ herbaceous perennials

:<.<-

no vegetation
Tillandsia spp.

Figure 1. Vegetation zonation in the fog zone or lomas formation of coastal Peru.

the clouds, a fog zone develops with a stratus
layer concentrated against the hillsides (Fig.
2B). This fog, termed garua in Peru, is key to
the floristic diversity of the unusual desert plant
communities, termed lomas formations. In
Peru, we estimate there are nearly 70 discrete
localities supporting lomas vegetation (Fig. 3),
including several offshore islands (e.g., Islas de
Las Viejas, San Gallan, San Lorenzo). The ac-
tual area covered by vegetation, even during pe-
riods of maximum development, is probably
less than 8,000 hectares. The vegetation of the
lomas formations of Peru is unique and com-
posed of many species that occur only in these
small desert oases.

Lomas Vegetation

Lomas communities occur as islands of vege-
tation separated by varying distances of hyper-
arid habitat devoid of plant life. Since plant
growth is dependent on available moisture and
the drought tolerance of individual species, a
combination of climate, physical topology, and

the ecophysiology of each species of plant ul-
timately determines community composition.
The individual formations are highly variable
and consist of mixtures of annuals, short-lived
perennials, and woody vegetation. Current es-
timates of the flora of the Peruvian lomas in-
clude over 815 species distributed in 357 genera
and 85 families of flowering plants. The distri-
bution patterns of these species can be roughly
grouped into broad categories, including (1)
pan-tropical or weedy species, (2) long-distance
disjunctions from the Sonora Desert or Baja
California, (3) species disjunct from the adja-
cent Andean Cordillera, and (4) plants restricted
to the coastal deserts, sometimes in a single lo-
cality. Endemism at the level of species often
exceeds 40% in individual lomas communities.
The greatest number of endemics are found in
southern Peru between 15S and 18S latitude
and include both endemic genera, such as Is-
laya (Cactaceae), Weberbaueriella (Fabaceae),
Mathewsia, and Dictyophragmus (both Brassi-
caceae), and endemic species within genera,
such as Ambrosia (Asteraceae), Argylia (Big-
noniaceae), Astragalus (Fabaceae), Cristaria
and Palaua (both Malvaceae), Calceolaria

Figure 2. Atacama and Peruvian desert communities. A. Flat inland desert region devoid of plants. B. Stratus
clouds impacting the headlands where lomas formations develop. C. Rainstorm above Cerro Campana in the northern
Peruvian coastal desert during the 1997-1998 El Nino event, February 1998. D. Cerro Cabezon during the 1997-
1998 event. E. Corn cultivated within the lomas formations of Cerro Cabezon in northern Peru, January 1998. F.
Goats grazing on the abundant vegetation at Mejfa during the El Nino event, October 1983. G. A carpet of Nolana
humifusa on the upper slopes of Cerro Cabezon, January 1998. H. Flowering individual of Nolana humifusa at Cerro
Cabezon.

The Lomas Formations of Coastal Peru

M. O. Dillon et al.

ACHENOO
MEJIA '.

-^ V3AMA GRANDE

200\ 400 690 \800km

Figure 3. Geographic features, including lomas formation localities, in the Atacama and Peruvian deserts.

(Scrophulariaceae), Tiquilia (Boraginaceae),
Jaltomata, Leptoglossis, and Nolana (all Sola-
naceae), and Eremocharis (Apiaceae).

We have examined patterns of similarity
within the overall flora of the lomas formations
and have found that the coastal deserts of west-

ern South America are not uniform (Duncan
and Dillon 1991; Rundel and Dillon 1998; Run-
del et al. 1991). Our analysis supports three flo-
ristic segments that appear to have independent
histories: (1) a northern Peruvian unit from
755'S to 12S latitude, (2) a southern Peruvian

The Lomas Formations of Coastal Peru

unit from 12S to 18S latitude, and (3) a north-
ern Chilean unit from 20S to 28S. The area
between 1 8S and 20S is nearly devoid of veg-
etation (Rundel et al. 1991) and is suggested to
have been a barrier to coastal dispersal for an
extended period (Alpers and Brimhall 1988).
Only 1 15 species, or ca. 12% of the total desert
flora of 1,350 vascular plant species, are re-
corded from both sides of 18S (roughly the
Peru-Chile border). When widespread weeds
are eliminated from that total, less than 6% of
the native species are known from either side.

Although the richness of the marine environ-
ment would have provided early man with a
primary source of sustenance (Keefer et al.
1998), the lomas formations could also have
acted as an important source of fresh water,
food, and construction materials for early coast-
al visitors and inhabitants (Lanning 1965). The
presence of vegetation, often forageable, would
have attracted the native camelids, for example,
guanaco, and deer, both of which were game
for early man. Supplies of seeds and insects
would have made lomas sites havens for native
bird species. The native flora does contain some
edible fruits; for example, Jaltomata and Ly-
copersicon, both members of the Solanaceae
family, have tomato-like, edible berries. Edible
roots from diverse plant families might also
have provided some nourishment that could
have been utilized periodically, for example,
Argylia radiata (Bignoniaceae), Begonia octo-
petala (Begoniaceae), Oxalis dombeii (Oxali-
daceae), Solarium montanum (Solanaceae), and
Tropaeolum peltophorum (Tropaeolaceae). Ag-
riculture may also have been practiced at some
locations, especially during exceptional years
associated with El Nino events. Today, crops
are cultivated in the lomas formations when op-
portunities are provided by increased available
moisture. Corn was planted at Cerro Cabezon
(Fig. 2E) in northern Peru during an El Nino
event in March 1998, and both corn and wheat
were cultivated in the lomas between Moque-
gua and Tacna in 1983.

The influence of man on the lomas forma-
tions, especially over the last 1500 years,
should not be underestimated. Many native
woody species have been severely depleted for
firewood and construction. It may be assumed
that native tree species, such as Caesalpinia
spinosa (tara), Carica candicans (mito), or
Myrcianthes ferreyrae, had wider distributions
and larger populations prior to the arrival of

man. The removal of woody vegetation almost
certainly would have changed the extent of her-
baceous plants. Building in many coastal areas
has replaced lomas habitat with homes and fac-
tories. Movement of livestock between the in-
terior and the coast has led to the introduction
of many Andean weeds (Sagastegui and Leiva
1993). The historical introduction of alien or
exotic species, such as Australian trees (Euca-
lyptus and Casuarina), has changed the char-
acter of the landscape. Perhaps the worst plague
that man has set upon the lomas formations
since the arrival of Europeans was the intro-
duction of herbivores such as goats (Fig. 2F),
which are very destructive to the native com-
munities.

El Nino Events

In our search for the forces that act on the
coastal regions, we identified short-term cli-
matic fluctuations of El Nino events (5- to 50-
year cycles) as important seasonal influences on
the coastal region. The physics behind the El
Nino-Southern Oscillation (ENSO) phenome-
non is complex and represents a worldwide
weather perturbation. El Nino conditions pre-
vail when the normally cold waters of the coast
of western South America are displaced by a
warmer, western Pacific surface and subsurface
body of water that stimulates brief periods of
heavy rainfall (Fig. 2C) and relatively high tem-
peratures. This influx of available moisture has
profound effects within the lomas formations
(Fig. 2D) and has undoubtedly helped shape
their composition and structure. Primarily, this
moisture stimulates massive germination of
seeds, leading to large blooming events that re-
plenish seed banks for annual and perennial
plants. These events also provide opportunities
for seed dispersal and establishment, which
would expand distributions under favorable
conditions (Fig. 2G). The impact of El Ninos
on these communities is obvious (Dillon and
Rundel 1990), and one can only wonder what
the coastal vegetation would resemble in the ab-
sence of these conditions. Potentially, levels of
floristic diversity would be much lower and mi-
gration and establishment more difficult. In the
western Pacific, the reverse effects of recurrent
droughts and rainfall variability have been im-

M. O. Dillon et al.

plicated in the evolution of vegetation patterns
in Australia (Nicholls 1991).

El Nino events have been recorded in both
historical (Quinn and Neal 1987) and Holocene
periods (DeVries 1987; Fontugne et al. 1999;
Magilligan and Goldstein 2001; Rodbell et al.
1999; Sandweiss et al. 1996, 1999, 2001). Lon-
ger-term records of El Nino events are more
difficult to detect and interpret (Moseley 1987).
Recently, Hughen et al. (1999) detected vari-
ability in growth patterns in fossil coral which
they interpreted as representing El Nino-like
conditions that may have existed for at least
124,000 years. Our studies of modern vegeta-
tion do not allow for estimations of the onset
of El Nino conditions, but regardless of their
age, they have undoubtedly played an important
role in shaping the present coastal communities.

Glacial Cycles and Sea Level
Changes

Longer-term climatic change associated with gla-
cial cycles (13,000- to 200,000-year cycles) pre-
dates the arrival of man and the first El Nino and
would have been active throughout the Pleisto-
cene (1.8 million years ago). It is estimated that
there have been at least 20 glacial events during
the Pleistocene, each with cycles of approximate-
ly 200,000 years. The formation of glaciers on
mountains and poles has caused sea levels to fluc-
tuate dramatically (Matthews 1990). Estimates of
sea level fluctuation range between 400 and 750
feet (120-230 m), and this lowering would have
significantly changed the position of the seashore
in relation to that of today. This drop would have
exposed a considerable area of the continental
shelf and displaced lomas plant communities, es-
pecially between 5S to 15S latitude (Fig. 4).
This would have resulted in species shifting their
ranges in relation to the near-ocean environments,
adapting to changing conditions in situ, or under-
going range reductions and extinction. Glacial cy-
cles would also have had a profound influence on
the flora and fauna of the coastal deserts by pro-
viding geographic isolation at certain times, and
at other times, opportunities for merging species,
thereby allowing for gene exchange. The last gla-
cial cycle ended ca. 13,000 years ago, and post-
glacial vegetation patterns are comparable to
those we find today (Dillon et al. 1995).

Nolana Studies

Within the lomas formations, the genus Nolana
(Solanaceae-Nolaneae) stands out as one of the
most wide-ranging and conspicuous elements of
the flora (Tago-Nakazawa and Dillon 1999).
Nolana is a genus of ca. 85 species that is large-
ly confined to coastal Andean South America
from central Chile to northern Peru, with one
species endemic to the Galapagos Islands. It is
the only genus to be encountered in nearly all
lomas formations. Nolana species are often im-
portant members of their respective communi-
ties and dominate in the numbers of individuals
present. Their showy flowers are beautiful, and
species display various types of habits annu-
als, perennials, or shrubs and variable corolla
sizes and shapes (Fig. 2H). Ecologically, No-
lana species prefer arid and semi-arid habitats,
with their greatest concentration in near-ocean
habitats within a few kilometers of the shoreline
(Fig. 2G). The establishment of a phylogeny for
Nolana has provided a framework for testing
hypotheses of isolation events in desert com-
munities. The species distribution pattern in No-
lana is similar to that in the overall flora and
displays three distinctive units: northern Peru,
southern Peru, and northern Chile. Only four
species have distributions that span the 18-
20S gap. The presence of two major groups
(clades) in the genus Nolana, one Peruvian and
the other Chilean, points to long-term isolation
of the genus above and below 18S latitude.

Reliable data on speciation rates for desert
plants are largely lacking. However, the devel-
opment of endemic genera and species, and the
morphological and physiological adaptations
they manifest, support the hypothesis of long-
term aridity along the coast of Peru, at least
from 12S to 28S latitude (Rundel and Dillon
1998). The timing of vicariant events (separa-
tion) can be estimated with molecular diver-
gence data to establish a molecular clock (Tago
1999). For the genes investigated, all estimates
for the first appearance of Nolana are late Ter-
tiary (Miocene, 10.6-11.6 mya). These data
also suggest that TV. galapagensis potentially
reached the Galapagos Islands sometime be-
tween 4 and 8 mya (late Miocene to early Pli-
ocene). Because of character evolution in the
mainland members of Nolana, it appears that
N. galapagensis was pre-adapted to arid habi-
tats prior to its dispersal to the island chain
(Tago-Nakazawa and Dillon 1999). The geo-

The Lomas Formations of Coastal Peru

76 C

Figure 4. Bathometric diagram illustrating the continental shelf of Peru between 5S and 14S latitude. Stippled
area indicates the land exposed should there be a 100-meter drop in sea level. Between 14S latitude (Pisco, Peru)
and 28S latitude (northern Chile), the continental margin is very narrow.

graphic origin of this remote island endemic re-
mains a mystery, but comparative morphology
points to Chilean ancestors (Dillon, unpubl.).

Recent archeological findings from the north-
ern Atacama Desert have recorded Nolana
fruits (technically mericarps containing seeds)
in rodent middens dating to 35,000 years B.P.
(Betancourt et al. 2000). These mericarps are
comparable to those we find in this desert lo-
cality today. Therefore, the divergence data
from molecular studies and the presence of No-
lana in desert habitats for no less than 35,000
years suggest that 10,000 years ago, the overall

character of the coastal flora was similar to that
found today. The frequency of strong El Ninos
and demonstrated sea level changes suggest that
these phenomena have played a role in stimu-
lating evolution in the plants of the lomas for-
mations.

Conclusions

The vegetation of coastal Peru is largely re-
stricted to the lomas formations, a series of iso-

M. O. Dillon et al.

lated, fog-dependent plant and animal commu-
nities that are diverse and highly endemic. In-
dividual lomas localities have unique species
compositions and display disharmonic patterns
found in "true" insular communities. While the
aridity along the Peruvian coast is essentially
constant, with negligible rainfall, the topogra-
phy and geologic history combine to divide
coastal Peru into a northern unit, 755'S to 12S
latitude, and a southern unit, from 12S to 18S
latitude.

Given available paleoclimatic data and di-
vergence times suggested by molecular clock
calculations on gene sequences, it appears that
Nolana occupied coastal desert environments in
both Peru and Chile prior to the Pleistocene gla-
cial events. Further investigations will be nec-
essary to test hypotheses of the age for the de-
sert, but our preliminary studies point to west-
ern South America as an arid region of great
antiquity well over 35,000 years ago. It appears
that the flora of the lomas formations have been
shaped by the effects of short- and long-term
climatic changes and by the influence of man
and introduced animals. Our data suggest sta-
bilized aridity for coastal Peru since before the
arrival of its first inhabitants (10,000 years
ago), but with dynamic periods with much
greater available moisture (Sandweiss et al.
2001). Early man would have found an envi-
ronment with more trees and much denser veg-
etation, which could have provided valuable re-
sources in the inhospitable coastal desert.

Acknowledgments. M.O.D. acknowledges the
support of the National Science Foundation and
National Geographic Society for field studies
associated with El Nino events. S.L.G. thanks
the Field Museum Scholarship Committee for
financial support to visit the Field Museum. F.
Barrie, W. Burger, and P. Rundel provided con-
structive reviews that improved the manuscript.

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Response of a Land Snail Species (Bostryx conspersus} in the

Peruvian Central Coast Lomas Ecosystem to the

1982-1983 and 1997-1998 El Nino Events

Rina Ramirez, Saida Cordova, Katia Caro, and Janine Dudrez

Land snails are conspicuous inhabitants of the
lomas ecosystems, which are islands of vege-
tation in the Pacific coastal desert of South
America. The mollusks are adapted to survive
the extreme summer conditions of the lomas,
when the highest temperatures and the lowest
humidities are reached. Bostryx conspersus
(Sowerby, 1833; Mollusca, Bulimulidae) is the
most common species from the lomas of the
Peruvian central coast. In a year without an El
Nino event, individuals of B. conspersus aesti-
vate during the dry season (December-April)
buried in the ground, mainly next to perennial
plants. During the wet season the snails become
active again. We present our observations of
changes in snails' seasonal activity during the
1982-1983 and 1997-1998 El Nino events, oc-
curring within the lomas of Iguanil and Lachay
(Lima, Peru), respectively. The activity of B.
conspersus during the summer of those years
was unusual. The snails behaved as if it were a
wet season. They had successful recruitment
that led to a remarkable population explosion,
mainly due to the high humidity and increased
shelter. However, the response of B. conspersus
showed differences between the two El Nino
events, reflecting dissimilarities between the
starting time and duration of the sea-surface
temperature anomalies and the concomitant
weather variation in the lomas of the central
coast of Peru. The response of B. conspersus to
the seasonal changes during 1995 and the cold

year of 1 996 are contrasted with those of the El
Nino years.

Introduction

The coast of Peru is a desert. The terrestrial
biodiversity, mollusks in particular, is concen-
trated mainly in the lomas. The desert land-
scape changes drastically during El Nino
events, the oceanographic component of El
Nino-Southern Oscillation (ENSO), which has
affected the Pacific coast of South America
since 5800 B.P. (Sandweiss et al. 1999). The
lomas are spectacular ecosystems, islands of
vegetation that endure the harsh conditions of
dry summers and enjoy the humidity of the ad-
vective fogs coming from the ocean during the
winter. The resident fauna of the lomas is also
adapted to its seasonality (Aguilar 1954, 1985).
Similarly, the biota must be adapted to climatic
changes in the mid- and long term produced by
recurrent El Nino events or the species would
have become extinct. However, almost nothing
is known about the responses of terrestrial spe-
cies to El Nino events, compared to what is
known about the marine biota (Arntz et al.
1985; Arntz and Fahrbach 1996; Vegas 1985).
Among the fauna, land snails are conspicuous
inhabitants of the lomas, and because of their
low vagility, they are good animals in which to
study responses to El Nino events. Following

Response of a Land Snail Species (Bostryx conspersus)

\ 1

Figure 1. Map showing location of the study sites, Lachay and Iguanil, Peru.

an El Nino event (a phase with warm tropical
water), there is a phase with cold tropical water
called La Nina (Sandweiss et al. 1999), produc-
ing changes in the lomas weather as well. Our
study deals with the response of Bostryx con-
spersus (Sowerby, 1833) to the last two major
El Nino events (1982-1983 and 1997-1998)
and the 1996 La Nina event in the lomas of the
central coastal desert of Peru.

Materials and Methods

Study Site

Location. The two study sites are located in
the Department of Lima, Peru (Fig. 1 ). The lo-
mas of Lachay (1119'S, 7722'W), a national
reserve, are 105 km north of Lima City and 7
km from the seashore. The altitude is between
150 and 750 m. The lomas of Iguanil (1 123'S,
7714'W) are located southeast of Lachay and
103 km from Lima, 15 km from the seashore.
The altitude is between 250 and 750 m.

Climate. The climate of the lomas is season-
al, characterized by a dry season (December-
April) and a wet one, also called the "lomas
season" (late July-September). The other
months are transitional between seasons. Usu-
ally the highest temperatures (monthly mean:
20C) and the lowest humidities (79%-82%)
are reached during summer, contrary to what
happens during the wet season, when the mean
monthly air temperature is 15C, with very high
air humidity (Ordonez and Faustino 1983; Saito
1976; Torres 1985). The El Nino events change
this seasonal picture because of an increase in
precipitation as drizzle or summer precipitation
(Pinche 1994; Torres 1985).

During an El Nino event, the sea-surface
temperature increases abnormally above the
mean (Fig. 2). In the continental area, air tem-
peratures in the lomas also change, showing the
same tendency (Fig. 3). The same tendency was
also noticed in Lima City (Obregon et al. 1985).
Sea-surface temperature data corresponded to
mean monthly values from Puerto Chicama
(0742'S, 7927'W).

R. Ramirez et al.

Ja r M Ap My Jn J ASONDJaFMApMyJnJ A 3 O N D

---*--- 1982-83

1995-96

1997-98

Figure 2. Sea-surface temperature anomalies at the Puerto Chicama station, Peru (0742'S, 7927'W). The char-
acterization of years follows Aguilar (1990): El Nino events: >2.7 (extraordinary), 1.7-2.7 (strong), 0.8-1.6 (mod-
erate), 0.5-0.7 (weak). A normal year is 0.6 to 0.4. La Nina events: 0.9 (cold year), 1.8 (very cold year).

Lomas of Iguanil During 1982-1983. The
micrometeorologic data were recorded by CIZA
(Arid Zones Research Center, Agrarian Univer-
sity, La Molina, Peru). Observations were taken
during 10 hours of 1 day a month, at altitudes
of 300 and 500 m. We used the mean values of
the day for air temperature, relative humidity,
and soil humidity. Precipitation values are from

Torres (1985) (Table 1). The climatogram is
shown in Figure 4.

Lomas of Lachay During 1995-1998. The
data were acquired from SENAMHI (Servicio
Nacional de Meteorologfa e Hidrografia del
Peru). The data for both air temperature and
relative humidity are mean monthly values; pre-

SST (1982-83) SST (1995-96)

* SST (1 997-98) - - - *- - - AT (Iguanil 1 982-83)

- - o_ . AT (Lachay 1 995-96) - - A - - AT (Lachay 1 997-98)

Figure 3. Comparison of sea-surface temperatures at the Puerto Chicama station and air temperatures at two
lamas along the central coast of Peru.

Response of a Land Snail Species (Bostryx conspersus)

TABLE 1. The lomas of Iguanil: Meteorologic and biologic data (1982-1983).

Month, year

Air temp.

(C)

Relative
humidity (%)

Soil humidity
(%)

Precipitation
(mm)*

Ground cover

(%)*

B. conspersus
(no. snails/
9400 m 2 )

Jan. '82 (Ja2)

23.99

77.49

1.18

0.81

Mar. '82 (M2)

1.05

May '82 (My2)

22.6

72.15

0.85

2.55

July '82 (J2)

16.05

85.08

0.82

5.025

Aug. '82 (A2)

17.89

86.62

5.09

3.3

Sept. '82 (S2)

Oct. '82 (O2)

18.42

80.12

3.27

38.65

Nov. '82 (N2)

12.5

Dec. '82 (D2)

24.88

73.76

1.895

Jan. '83 (Ja3)

26.13

76.34

2.49

44.15

Feb. '83 (F3)

24.72

80.4

2.815

64.3

Mar. '83 (M3)

27.57

65.07

0.915

45.8

Apr. '83 (Ap3)

23.59

93.44

6.83

May '83 (My3)

21.59

94.14

3.2

47.9

June '83 (Jn3)

20.93

96.06

75.65

July '83 (J3)

16.09

93.65

8.5

118

Sept. '83 (S3)

16.66

97.17

54.5

* After Torres (1985).

cipitation is the cumulative monthly value (Ta-
ble 2). The climatogram is shown in Figure 5.

Vegetation. The lomas vegetation consists of
herbaceous species that are green mainly during

the wet season, and also perennial species
(shrubs and trees) that adapt to the seasonality
of the lomas (Dillon and Rundel 1989; Ferreyra
1993; Ono 1986). In general, changes in climate
conditions during the year modify the landscape

100
95
90
85
80
75
70
65
60

ap3

19 24

Temperature (C)

Figure 4. Climatogram of the lomas of Iguanil, Peru, 1982-1983.

R. Ramirez et al.

TABLE 2. The lomas of Lachay: Meteorologic and biologic data (1995-1998).

Month, year

Air temp. Relative humidity Precipitation
(C) (%) (mm)

RGC* B. conspersus
(%) (no. snails/400 m 2 )

Jan. '95 (Ja5)

21.2

3.5

Feb. '95 (F5)

22.1

0.5

Mar. '95 (M5)

21.2

1.4

Apr. '95 (Ap5)

19.9

May '95 (My5)

18.4

0.7

June '95 (Jn5)

July '95 (J5)

13.5

19.9

Aug. '95 (A5)

13.2

4.7

1271

Sept. '95 (S5)

17.2

1492

Oct. '95 (O5)

14.5

10.5

456

Nov. '95 (N5)

15.8

1.6

681

Dec. '95 (D5)

16.5

1.4

207

Jan. '96 (Ja6)

18.4

1.1

Feb. '96 (F6)

22.5

Mar. '96 (M6)

22.1

Apr. '96 (Ap6)

19.3

0.4

May '96 (My6)

16.4

June '96 (Jn6)

13.2

278

July '96 (J6)

14.2

Aug. '96 (A6)

368

Sept. '96 (S6)

147

Oct. '96 (O6)

Nov. '96 (N6)

15.7

Dec. '96 (D6)

18.2

Jan. '97 (Ja7)

Feb. '97 (F7)

22.2

Mar. '97 (M7)

22.6

May '97 (My7)

July '97 (J7)

19.1

10.7

Aug. '97 (A7)

18.1

31.7

211

Sept. '97 (S7)

18.1

40.4

1345

Oct. '97 (O7)

17.4

28.4

927

Nov. '97 (N7)

18.9

20.4

373

Dec. '97 (D7)

21.2

65.2

237

Jan. '98 (Ja8)

103.1

476

220

Feb. '98 (F8)

23.6

47.5

980

552

Mar. '98 (M8)

23.7

724

637

Apr. '98 (Ap8)

22.3

2.5

321

146

May '98 (My8)

18.9

16.5

325

897

June '98 (Jn8)

16.4

34.5

529

1587

July '98 (J8)

15.4

16.4

907

1473

Aug. '98 (A8)

46.4

763

5448

Sept. '98 (S8)

14.1

28.2

806

9369

* Reiterated ground cover.

from a brown color (almost zero ground cover)
during summer to a vivid green color during
winter, when the annual species provide a large
amount of ground cover. However, during El
Nino events, the timing of these changes is very
different, as was observed during the 1982-
1983 El Nino event in Iguanil (Torres 1985) and
in 1997-1998 in Lachay (Arana et al. 1998).
Ground cover data for Iguanil are from Torres
(1985). We used the mean values for each
month (Table 1). For Lachay, we used the "re-

iterated ground cover" figure obtained by the
botanical team from the Museum of Natural
History of the University of San Marcos (Table
2).

Mollusks. Bostryx conspersus (Sowerby,
1833; Gastropoda, Bulimulidae) has a globose
and rather thin shell of about 15 mm height
(Fig. 6c). It has been recorded in the lomas of
central and southern Peru (Departments of
Lima and Arequipa) (Aguilar and Arrarte 1974;

Response of a Land Snail Species (Bostryx conspersus)

3
I

100
95
90
85

SL 80

Air Temperature (C)

Figure 5. Climatogram of the lomas of Lachay, Peru, 1995-1998.

Figure 6. Some lands snails from Lachay: a, Succinea peruviana; b, Bostryx modestus; c, Bostryx conspersus;
d, Scutalus proteus; e, Scutalus versicolor; f, Bostryx scalariformis. (Photograph by B. Collantes.)

R. Ramirez et al.

Weyrauch 1967). Individuals of B. conspersus
aestivate during the dry season buried in the
ground, mainly next to perennial plants. They
are also found buried adjacent to rocks, or in
small interstices between them. During the wet
season the snails become active again (Pulido
and Ramirez 1982; Ramirez 1988).

B. conspersus shares the lomas with other
land snail species. For example, in Lachay the
following native species are also present: Bos-
tryx aguilari Weyrauch, 1967; B. modestus
(Broderip, 1832) (Fig. 6b); B. scalariformis
(Broderip, 1832) (Fig. 6f); Scutalus proteus
(Broderip, 1832) (Fig. 6d); Scutalus versicolor
(Broderip, 1832) (Fig. 6e); Succinea peruviana
Philippi, 1867 (Fig. 6a); and the two minutes
Pupoides paredesi (d'Orbigny, 1835) and Gas-
trocopta pazi (Hidalgo, 1869), as well as the
introduced Helix aspersa (Miiller, 1774).

Monitoring

Lomas of Iguanil. The study area in the lo-
mas of Iguanil was the Quebrada El Granado.
The quantitative survey was carried out 1 day
a month in a transect of 20 X 470 m (= 9,400
m 2 ) between 420 and 600 m above sea level.
The transect is located in a hilly area along the
center of the ravine, with perennial vegetation
(mainly shrubs, e.g., Trixis cacalioides,
Ophryosporus pubescens, Cestrum auriculatus,
Dicliptera tomentosa, Heliotropium spp.).
There is also annual herbaceous vegetation
(e.g., Nicotiana paniculata, Chenopodium pe-
tiolare, Oxalis sp., Sicyos baderoa). The survey
was carried out from May 1982 to July 1983
(except June 1983). The search for unburied
snails was conducted by direct observation. R.
Ramirez carried out this part of the work as a
member of a team of the CIZA/UNA-La Mo-
lina (Lima, Peru), which conducted botanical,
faunal, and anthropological research in several
lomas of the central coast of Peru during the
1970s and 1980s.

Lomas of Lachay. The Museum of Natural
History of the University of San Marcos, Lima,
Peru, has been engaged in monitoring vegeta-
tion and mollusks to track El Nino events in the
lomas ecosystems as part of the RIB EN study
(Red de Impacto Biologico de los Eventos El
Nino, CONCYTEC) from May 1995 to the
present.

For a quantitative survey, we selected an area
dominated by shrubs (e.g., Ophryosporus pe-
ruvianus, Senecio spp., Trixis cacalioides, Cro-
ton spp.), including annual herbaceous vegeta-
tion (e.g., Loasa urens, Nicotiana paniculata,
Urocarpidium peruvianum, Nolana humifusa).
Monitoring of the land snails at the two lomas
was carried out as independent projects. Al-
though we tried to maintain the same area in
Lachay for quantitative sampling as in Iguanil,
it did not work as well because of the greater
abundance of B. conspersus. We delimited four
plots of 10 X 10 m (= 400 m 2 ), 50 m apart,
along a transect between 470 and 550 m in al-
titude. We counted the unburied snails observed
in 1 day per month, except during 1998, when
we needed an extra day because of the high
number of individuals and the exuberant her-
baceous vegetation. The data we present here
are from July 1995 to September 1998. No sur-
vey was conducted in July 1996 or in January,
February, April, or June of 1997.

Principal Component Analysis

We used principal component analysis (PCA) to
ascertain whether changes in monthly density
of B. conspersus along with changes in air tem-
perature, relative humidity, or ground cover
could help discriminate El Nino months from
non-El Nino months. We did not use the pre-
cipitation data, which were incomplete. Micro-
soft Excel was used for data management and
the analyses were performed using SPSS (Sta-
tistical Package for the Social Sciences, V05)
software.

Results

Iguanil (1982-1983)

The monthly variation in number of unburied
individuals of Bostryx conspersus in the lomas
of Iguanil did not show the same trend from
one year to the next. In 1982 the snails were
active during part of the winter and spring,
whereas in 1983 the activity period started ear-
lier, at the end of the summer. The highest num-
ber of snails recorded in 1983 was recorded ear-
lier, in July, and was almost threefold (118 in-
dividuals in 9,400 m 2 ) the number recorded in

Response of a Land Snail Species (Bostryx conspersus)

1982 (October, 43 individuals) (Table 1, Fig.
7a).

In relation to the differences among survey
months, PCA of data on snails, ground cover,
air temperature, and relative humidity generated
four components to explain the total variance.
The PCI analysis explained 62.157% of the
variance, with variation in number of snails
having the greatest influence, followed by var-
iation in the relative humidity. In the PC2 anal-
ysis (28.492%) ground cover was the principal
factor, followed rather distantly by air temper-
ature (Table 3). In the scatter diagram of PCI
X PC2, three groups of months are formed,
with the months of the 1982-1983 El Nino ep-
isode in two of them (December 1982-March
1983, and May-July 1983) (Fig. 8).

Lachay (1995-1998)

During the almost 4 years of survey of B. con-
spersus in the lomas of Lachay, the higher num-
ber of active snails (unburied) per observation
period decreased from 1995 through 1997, but
in 1998 exceeded the highest counts of previous
years. The lowest numbers of snails occurred
during the summer of 1996 and the summer of
1997, corresponding to the aestivation period
(Table 2, Fig. 7b).

In relation to the differences among the sur-
vey months, PCA generated four components
to explain the total variance, of which the first
two accounted for 71.412% of the variance. In
PCI (52.046%), variation in relative humidity
had the greatest influence, followed by variation
in air temperature, while in PC2 (19.366%), the
number of snails and the ground cover were the
variables with greatest influence (Table 4). In
the scatter diagram of the first two components,
five groups of months were formed. Those of
the 1997-1998 El Nino segregated into two
groups (March-July-August 1997, and Septem-
ber-December 1997-January-April 1998); the
following months (post-El Nino) also formed a
separate group (June-September 1998). The
two other groups were formed by (1) August-
November 1995 and (2) December 1995-Jan-
uary-May 1996 and November-December
1996 (Fig. 9).

Discussion

Bostryx conspersus has seasonal behavior,
showing a clear response to the seasonal cli-
mate of the lomas ecosystem (Pulido and Ra-
mirez 1982; Ramirez 1988). The intensity of
change in the climatic regimen can be detected
from the variation in monthly number of un-
buried snails, as described here. El Nino events
change the seasonality of the lomas, mainly be-
cause of summer rains (Oka and Ogawa 1984;
Pinche 1994).

Climatologically, no one year was similar to
any other during the study (Figs. 4 and 5), nor
were the monthly density variations in active
land snails similar (Fig. 7). Analysis of the sea-
surface temperature anomalies at Puerto Chi-
cama during the periods of our studies (1982-
1983, 1995-1998) (Fig. 2; Quispe 1993) shows
that in this respect too, there were not two equal
years (Rasmusson and Arkin 1985). This dem-
onstrates the direct influence of the ocean on
the climate of the lomas as well as other con-
tinental areas (Obregon et al. 1985). Likewise,
we cannot say that during the period of survey
in the lomas of Lachay there was a "normal"
year for the lomas. On the contrary, we had the
El Nino years (1997-1998), an unusually cold
year (La Nina, 1996), and a mixed warm and
mildly cold year (1995).

Using the data of B. conspersus along with
those of air temperature, relative humidity, and
ground cover, then performing a principal com-
ponent analysis, we arrived at assemblages of El
Nino months that were arranged in a different
way from those of non-El Nino ones. At the
same time, months during El Nino events were
segregated into two groups; we call them the first
phase and the second phase of El Nino (Figs. 8
and 9). Checking the anomalies of sea-surface
temperature, it is also possible to see that the two
El Nino events were indeed different.

The 1982-1983 and 1997-1998 El Nino ep-
isodes are considered to be extraordinary be-
cause the sea-surface temperature anomalies
differed by more than 2.7 SD (Fig. 2) (Aguilar
1990; Quinn 1993). At the same time, the El
Nino events differed in starting point and in du-
ration. For example, in the 1982-1983 El Nino
event, warm water reached the central coast of
Peru late in 1982 November in Callao (Go-
mez 1985) and did not affect the wet season
of the year very much. B. conspersus showed a
typical seasonal behavior during that year. The

R. Ramirez et al.

140
120 -I
100

10000

1000
o

1 100

b)[

O Lachay 95-96

Lachay 97-98

Figure 7. Monthly density of unburied individuals of Bostryx conspersus in two lomas on the central coast of
Peru: a, Iguanil; b, Lachay.

second instance of warming of the sea-surface
water occurred during the fall of 1983 April-
July (Zuta et al. 1985) which brought more
precipitation to the lomas, marking an early be-
ginning of the wet season in 1983 (Fig. 10). The
usual brown landscape of the summer was re-
placed by a nice carpet of herbaceous vegeta-
tion (Torres 1985). The population of B. con-
spersus from the lomas of Iguanil also respond-

ed to the quasi-lomas season, the difference be-
ing that the air temperatures were higher than
during the winter wet season (Fig. 4). The bi-
ological impact on the snails was positive; the
snails awoke earlier from the aestivation period,
and the recruitment was successful (Ramirez
1984). The population reached the levels of the
previous wet season very early (Fig. 7). A pos-
sible reason for this could be the survival of

TABLE 3. Results of PCA for the lomas of Iguanil (1982-1983).

Initial Eigenvalues

Compo-

% of

Cumula-

Component

nent

Total

Variance

tive %

Variables

2.486

62.157

Air temperature

-0.801

0.561

0.165

0.127

1.140

28.492

90.649

Relative humidity

0.872

-0.197

0.444

0.052

0.332

8.302

98.951

Ground cover

0.495

0.860

0.074

-0.099

0.042

1.049

100.000

Bostryx conspersus

0.916

0.214

-0.319

0.115

Response of a Land Snail Species (Bostryx conspersus)

-2

-1

PCI (62.157%)

Figure 8. Plots of the first two principal components for the months May 1982 to July 1983 for the lomas of
Iguanil.

more eggs and snails (especially just hatched
and juveniles) than usual (Ramirez 1984) be-
cause of the high humidity (the main cause of
death is desiccation [Pollard 1975]) and more
available shelter (Lomincki in Pollard 1975) be-
cause of the high amount of annual vegetation.
The two instances of sea-surface warming
during the 1997-1998 El Nino event occurred
earlier than those of the 1982-1983 El Nino
event. The first arrival of the warm water was
early during the fall of 1997 (Fig. 2). The whole
year was abnormally warm in the lomas, and
during the winter the high relative humidity val-
ues characteristic of the "lomas season" were
never reached; the contrary happened during
the late spring, which had high relative humid-
ity values, as shown in the climatogram for La-

chay (Fig. 5). The characteristic herbaceous
vegetation of the wet season was negatively af-
fected. For example, Isemene amancaes had
both a late beginning and a short development
period during 1997 (Agiiero and Suni 1999).
The population of B. conspersus was also neg-
atively impacted. Most of the snails stayed bur-
ied, and those that "woke up" were more ex-
posed to desiccation. As a consequence, the re-
cruitment was very poor (Fig. 1 1 ). The second
occurrence of warming of the 1997-1998 El
Nino event was at the beginning of the summer
of 1998 (Fig. 2) and brought an unusual amount
of water to the lomas (Fig. 12), extending the
late wet season of 1997 into the summer of
1998. Here the impact of the El Nino event was
positive for B. conspersus, which showed a

TABLE 4. Results of PCA for the lomas of Lachay (1995-1998).

Initial Eigenvalues

Compo-

% of

Cumula-

Component

nent

Total

Variance

tive %

Variables

2.082

52.046

Air temperature

-0.707

0.218

0.622

0.255

0.775

19.366

71.412

Relative humidity

0.833

0.160

-0.076

0.524

0.704

17.602

89.014

Ground cover

0.698

0.578

0.288

-0.308

0.439

10.986

100.000

Bostryx conspersus

0.633

-0.606

0.478

-0.064

R. Ramirez et al.

-2

-1

PCI (52.046%)

Figure 9. Plots of the first two principal components for the months July 1995 to September 1998 for the lomas
of Lachay.

population explosion. The recruitment was very
successful; and that, along with the high hu-
midity and exuberant herbaceous vegetation
(Arana et al. 1998, 1999), led to a high survival
rate among the snails.

The cold year of 1996 (La Nina) had a rel-
atively negative impact on B. conspersus com-
pared with the maximum number of snails
counted in the 1995 "wet season." The weather
was colder and drier than during the other years

(Figs. 5 and 12). The mortality rate of individ-
uals of all size classes was high, and the re-
cruitment was poor (Fig. 1 1 ; Ramirez et al.
1999). Affected in this way, the population ex-
perienced an El Nino the following year (1997),
with a hot winter and without the characteristic
high humidities (Fig. 5), depleting the popula-
tion even more. Finally, the arrival of the sec-
ond phase of the 1997-1998 El Nino event in-
jected some life into B. conspersus. The range

10 -,
9

! ?:

10
9
8 ^
7

c 6
o

j= 5

a 4

5 E
4 I

o 3^
Q- 2

^>'

, ^
\

3 o
2 W

1 -

*^ v\ J ^"1 ^r* fiiL-J *^ w\ J ^5
XT V*^ ^ oP ^J
\

\=n PRECIPITATION (mm)

-o SOIL HUMIDrTY (%)

Figure 10. Precipitation and soil humidity in the lomas of Iguanil, 1982-1983 (measured 1 day per month).

Response of a Land Snail Species (Bostryx conspersus)

10000

1000

100

>15mm

10.1 -15mm -A-5-10mm

-<5mm

Figure 11. Structure of the population of Bostryx conspersus by size classes from August 1995 to September
1998 in the lomas of Lachay. The El Nino event occurred from May 1997 to April 1998. (After Ramirez et al. 1999.)

of the population expanded as far as the her-
baceous vegetation did. The post-El Nino
months following the 1997-1998 event coincid-
ed with the 1998 wet season, which resulted in
an even higher density of active B. conspersus.
This was probably also the case for 1995 (end

of a weaker but much longer-lasting El Nino
than the two episodes analyzed here). Precipi-
tation and ground cover were greater than in
1996 (Table 2, Fig. 12), and B. conspersus
reached higher densities than in 1996 and 1997
(Figs. 7b and 9).

100

c
"5.

. 40

. . .1,

* * >

b <<

> * ^ ^ > * *

Lachay (1995-96)

D Lachay (1997-98)

Figure 12. Precipitation in the lomas of Lachay, 1995-1998 (cumulative monthly values).

R. Ramirez et al.

Thus, although the two El Nino episodes dif-
fered from each other, they were similar in that
their second phase had a positive impact on the
biota. The increase in humidity led to an in-
crease in herbaceous vegetation, and both of
these factors contributed to an increase in the
population of B. conspersus. At the same time,
predation on this population, mainly by rodents
and birds, also increased (Ramirez et al. 1999).

Acknowledgments. The work carried out on
the lomas of Iguanil was possible thanks to the
Arid Zones Research Center of the Agrarian
University (CIZA-UNA, La Molina, Peru). Di-
ana Silva y Juan Torres facilitated the work at
Iguanil. The monitoring of land mollusks on the
lomas of Lachay was made possible with the
aid of the American States Organization
(through RIBEN-CONCYTEC), the University
of San Marcos (FEDU-UNMSM), and the Na-
tional Council of Science and Technology
(CONCYTEC). We are grateful to the Institute
Nacional de Recursos Naturales for permits to
perform research in the National Reserve of La-
chay. Jose Arenas, Sergio Cano, Doris Florin-
dez, Marisa Ocrospoma, and Maria Samame
participated enthusiastically in the fieldwork,
and Asuncion Cano and Cesar Arana provided
the data on ground cover. Finally, we thank Ser-
gio Solari and Sonia Valle, who helped prepare
the illustrations.

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Debris-Flow Deposits and El Nino Impacts
Along the Hyperarid Southern Peru Coast

Luc Ortlieb and Gabriel Vargas

The coastal regions of Ecuador, Peru, and Chile,
which today experience the strongest meteoro-
logic and oceanographic impacts of El Nino,
are also the areas where paleoclimatologic re-
search is likely to yield relevant information
about former El Nino processes. The extreme
aridity that characterizes the coast of southern
Peru and northern Chile is favorable for the rec-
ord of episodic rainfall events that induce floods
and debris flows and the subsequent preserva-
tion of these deposits. This chapter compiles
available instrumental, documentary, and geo-
logic data on such deposits formed along the
coast at 17-18S latitude and discusses the re-
lationships that can be inferred between dated
debris-flow deposits and the occurrence of El
Nino events. The approach thus involves an
analysis of temporal correlations between El
Nino events, debris-flow episodes, and instru-
mental measurements of rainfall data during the
last several decades. This analysis shows a
weak statistical correlation between monthly or
yearly rainfall amount and the warm phase of
El Nino-Southern Oscillation (ENSO), but also
that strong rainfall, sufficient to provoke debris
flows, generally occurs during El Nino years.
Documentary data from the last few centuries
also tend to indicate that heavy rainfall episodes
along the coast of southern Peru have common-
ly occurred during El Nino years, even though
many El Nino years did not experience rains.
We conclude that, for at least the last few cen-
turies, El Nino conditions have been favorable
for the formation of exceptionally short-lived
but intense rainfalls, but that these conditions
are not sufficient per se. Several regional and
local meteorologic mechanisms and situations

are apparently involved in the episodic occur-
rence of strong rainfalls and debris-flow activity
along the coast of southern Peru.

Debris-flow activity during the early Holo-
cene and at the end of the Pleistocene, when
regional hydrologic conditions were different
than at present, is more difficult to interpret in
relation to ENSO. Unlike previous authors, we
consider that debris-flow deposits formed prior
to the mid-Holocene do not constitute strong
enough evidence for past El Nino conditions.
Similarly, we presume that lack of debris-flow
evidence during a given time period cannot be
taken as an indication that no El Nino events
occurred during that period. Until we have a
better understanding of the meteorologic pro-
cesses driving exceptional intense rainfalls in
the area and of the paleohydrologic regime, it
would be misleading to infer the existence of
El Nino, or La Nina, conditions from the exis-
tence of debris-flow deposits in this particular
region.

The Relevance of Paleo-ENSO
Studies

El Nino Southern Oscillation, or ENSO, is the
main source of global ocean climate variability
on an interannual time scale. Understanding the
variability of ENSO through geologic time is
necessary to determine the boundary conditions
that drive the phenomenon, to examine the in-
terrelationships between this mode of ocean cli-
mate variability and other, longer-term sources
of climate change, and to constrain coupled
oceanic-atmospheric models. There is also

Debris-Flow Deposits and El Nino Impacts

strong societal interest in improved forecasting
of El Nino events and in estimating the intensity
and frequency of future ENSO events under
conditions of global warming. Moreover, stud-
ies of the evolution of the dynamics of the
ENSO trough time are necessary to better un-
derstand the influence of the ocean climate sys-
tem on the development of different cultures
around the world.

Because instrumental records have been
maintained for only a short time, whereas cli-
mate modelers require longer-term records,
there is a growing need for paleo-ENSO proxy
records such as coral reef sequences, ice cores,
dendroclimatic analyses, lacustrine and alluvial
sedimentary sequences, beach ridge series, and,
for the last few centuries, documentary data.
These different proxy records generally aim to
reconstruct the frequency and intensity of for-
mer El Nino events the warm phase of ENSO.
Up to now, however, none of these records by
itself has yielded a complete series of El Nino
occurrences. For instance, Quinn and collabo-
rators (Quinn et al. 1987; Quinn and Neal 1992;
Quinn 1993) provided historical El Nino se-
quences based on documentary data that have
been widely used by ENSO researchers. But
other researchers (Hocquenghem and Ortlieb
1992; Whetton and Rutherfurd 1994; Whetton
et al. 1996; Ortlieb 1998, 1999, 2000; Ortlieb
et al. 2002) have questioned the accuracy of
many so-called reconstructed El Nino events
between the sixteenth and the eighteenth cen-
turies. This is not surprising, because some of
the documentary data come from areas as far
away as the Nile delta, China, and South Amer-
ica, where ENSO teleconnections are moderat-
ed by other atmospheric and oceanic processes.
As a result, no consensus has been reached on
a historical El Nino (or ENSO) chronological
sequence prior to the instrumental record. At
longer time scales the problem is still more
acute, if for different reasons: the scarcity of
high-resolution sequences, geochronological
uncertainties, alteration or partial erosion of the
records, and so on. In all cases, for very recent
(documentary) or older (geologic) records, one
particular problem must be addressed: Which
regions record the former occurrences of the
phenomenon with highest reliability? How can
we be sure that a geographic area that today
satisfactorily registers ENSO anomalies also
did so in the past, under different regional and
global circulation patterns?

El Nino Manifestations in Peru and Chile

The El Nino phenomenon was first identified in
northern Peru, near the border with Ecuador
(Carranza 1891), as the combination of an
anomalous seasonal (summer) warming of the
coastal waters and heavy rainfall in the desert
of Sechura (4-6S). Later, it was observed
along the coast of southern Ecuador to central
Chile that the phenomenon is also characterized
by a lowering of the thermocline and the nu-
tricline and by a rise in sea level that may reach
several decimeters within several weeks. The
coast of northern Peru is where the El Nino
phenomenon provokes the highest sea level rise
(more than half a meter in 1982-1983), greatest
seawater warming (up to 10C at Paita, in
1982-1983), and greatest rainfall anomalies (lo-
cally up to 4,000 mm, compared to 100 mm
mean). It is thus natural that this region is fa-
vored in the search for paleo-El Nino evidence
(Quinn et al. 1987; DeVries 1987; Ortlieb and
Machare 1993; Machare and Ortlieb 1993).

Another favorable area that faithfully regis-
ters the occurrence and intensity of ENSO man-
ifestations is central Chile (Quinn and Neal
1983). Rutllant and Fuenzalida (1991) showed
that at least since the end of the nineteenth cen-
tury, the warm phase of ENSO is characterized
by an excess of winter precipitation and the
cold phase is generally marked by a deficit of
rainfall. Over the last 120 years, for which there
are reliable instrumental rainfall data, there is a
good correlation between El Nino in northern
Peru (during the austral summer) and central
Chile (during the preceding austral winter) (Ort-
lieb 1998, 1999, 2000; Ortlieb et al. 2002). This
coincidence reflects a teleconnection mecha-
nism involving large-scale atmospheric pro-
cesses in the eastern Pacific region (Caviedes
1981; Hastenrath 1985; Hamilton and Garcia
1986; Deser and Wallace 1987; Aceituno 1988,
1990; Philander 1991; Allan et al. 1996). It is
because of this teleconnection that Quinn et al.
(1987) and Quinn and Neal (1992) relied on
documentary data on historical climatic anom-
alies from either central Chile or northern Peru
to reconstruct past occurrences of El Nino
events. However, Ortlieb and co-authors (Ort-
lieb 2000; Ortlieb et al. 2002) noted that before
1817, very few heavy rainfall events recon-
structed from documentary evidence from
northern Peru and central Chile did coincide in
time. Ortlieb (1997, 1998, 2000) thus suggested

L. Ortlieb and G. Vargas

that the teleconnection mechanisms had possi-
bly been affected by other modes of climatic
variability, such as those related to the Little Ice
Age. This hypothesis remains to be further test-
ed, for example, by comparing with data from
tropical ice core and coral reef sequences.
Meanwhile, it is plausible that the regional te-
leconnections observed today may not have
been operating in past centuries and millennia.

When Did the El Nino Phenomenon Appear
in Peru?

In the last few decades, there has been some
discussion regarding the onset of the El Nino
system of climate variability in Peru. Sandweiss
and co-authors (Sandweiss 1986; Rollins et al.
1986; Sandweiss et al. 1983, 1996, 1999) pro-
posed that no ENSO manifestation was recorded
in Peru before the mid-Holocene and supported
the hypothesis that the onset of the El Nino oc-
curred at about 5000 B.P. This interpretation re-
lied heavily on observations that some warm-
water mollusks occurred in different localities
prior to 5000 B.P. (noncalibrated age) along the
coast of north-central Peru. The mentioned au-
thors suggested that a large reorganization of the
ocean-atmosphere circulation system in the east-
ern Pacific took place during the mid-Holocene.
They claimed that prior to 5000 B.P., the coastal
waters of that area were significantly warmer
than today, and that after the mid-Holocene, the
boundary between the cold Humboldt (Peru)
Current and the warm equatorial waters would
have moved northward by about 500 km, to
reach its present position (at about 5S).

Other researchers (DeVries and Wells 1990;
Diaz and Ortlieb 1993; Perrier et al. 1994; Bearez
et al. 2003) have not shared the interpretation that
coastal waters were warmer in the past in north-
central Peru and instead have argued that the
warm-water molluscan species were all lagoonal
forms that lived in protected, marginal lagoons
that provided a higher temperature than the open
ocean. Other biological proxy data also failed to
support the theory of a major shift of the bound-
ary between the cool Humboldt domain and the
warm equatorial waters. Perrier et al. (1994)
showed through stable isotope serial analyses that
Trachycardium shells from north-central Peru dat-
ed to 5500 B.P., 5800 B.P., and 6100 B.P. contained
growth irregularities similar to those observed to-
day in response to El Nino events, registering

short-term thermal anomalies of the water that
amounted to several degrees C (like those record-
ed after the very strong 1982-1983 El Nino
event). Furthermore, DeVries et al. (1997) argued
that it was precisely because the El Nino system
already existed before 5000 B.P. that the lagoons
which formed during mid-Holocene maximum
sea level, near 7000 B.P. (Wells 1988), could be
fed episodically with larvae of warm-water spe-
cies that normally live in the Panamic molluscan
Province (i.e., north of 6S). Similar conditions of
lagoonal environments that previously enabled the
survival of extralimital warm-water species have
also been found in deposits of prior interglacial
stages in southern Peru and northern Chile (Ort-
lieb et al. 1990, 1996; Diaz and Ortlieb 1993;
Guzman et al. 2001).

Recently, additional terrestrial proxy data have
tended to indicate that El Nino extended back to
the end of the Pleistocene, although with differ-
ent characteristics. Rodbell et al. (1999) reported
data from a high-elevation Andean lake in south-
ern Ecuador, whereas Keefer et al. (1998) pre-
sented data from alluvial and debris-flow depos-
its in southern Peru (Fig. 1). Both studies suggest
that ENSO mechanisms were not restricted to the
second half of the Holocene. However, both
studies relied on an interpretation of alluvial pro-
cesses in two quite different depositional envi-
ronments, and both assumed that present-day hy-
drologic phenomena linked to ENSO were also
operative at the end of the Pleistocene and in the
early Holocene.

Here we evaluate interpretations of climatic
significance of alluvial deposits formed in the
southernmost part of the Peruvian coastal des-
ert. To what extent can we assume, as Keefer
et al. (1998) did, that remnants of debris flows
and floods in the coastal region of southern
Peru were related to El Nino conditions in the
latest Pleistocene and early Holocene times?
The relationships between paleo-ENSO impacts
and alluvial and debris-flow deposits in the area
will be analyzed at different time scales with
different kinds of data: ( 1 ) for the last half-cen-
tury, using instrumental measurements; (2) for
the last few centuries, based on documentary
sources; and (3) for the last 12,000 years, using
radiocarbon-dated geologic deposits. Recently
acquired data from southern Peru are presented
and discussed with respect to other published
El Nino proxy data (Keefer et al 1998; Fontug-
ne et al. 1999).

Debris-Flow Deposits and El Nino Impacts

Piu

Lima
< 13mm

Iquique

Rainfall (mm)

V ^

JH : n tu

Antofagasta

H 1020-2030

^| 760-1020

1 510-760

( '

[250-510
1 0-250

< 13 mm /

\ \

_] iJ

Pacific Ocean

Ilo

Quebrada Tacahuay
j- 1 8S Punta El Ahogado
72W Quebrada Los Burros

Quebrada El Cation
100km

Hi"'
Rio San Jose

Figure 1. A. Location of sites studied in southern Peru and northern Chile, with indication of mean interannual
rainfall (modified from Kendrew 1961). B. Details of the coast of southernmost Peru, with localities studied.

El Nino Impact on Rainfall and
Debris-Flow Events in Southern
Peru During the Second Half of the
Twentieth Century

El Nino and Rainfall Anomalies in Peru

After the very strong 1982-1983 El Nino event,
which was characterized by a severe drought in
the southern half of Peru and on the Bolivian
Altiplano, many authors (e.g., Huaman Solis
and Garcia Pena 1985; Francou and Pizarro
1985; Garcia Pena and Fernandez 1985; Rope-

lewski and Halpert 1987; Thompson et al.
1984) considered that the precipitation deficits
in this area were typical of El Nino conditions.
At present it is considered that the relative
drought that was observed during El Nino years
may be more specific to the Andean part of
southern Peru, and not precisely specific to the
coastal region of southern Peru (Rome-Gaspal-
dy and Ronchail 1998). Recent analyses of in-
strumental rainfall data from the second half of
the twentieth century confirm that the positive
rainfall anomalies over the coastal regions of
Ecuador and northern Peru exhibit the only sta-

L. Ortlieb and G. Vargas

tistically significant correlation with El Nino
events within the region encompassing Ecuador,
Peru, and Bolivia (Aceituno 1988; Rossel 1997;
Rome-Gaspaldy and Ronchail 1998; Rossel et
al. 1998). Analysis of monthly rainfall data be-
tween 1960 and 1990 indicates that only the
coastal area of northern Peru (Piura region)
shows a positive correlation between rainfall
and the warm phase of ENSO, and intensified
drought during the cold phase of ENSO (La
Nina) (Rome-Gaspaldy and Ronchail 1998).
More specifically, no clear correlation between
rainfall anomalies and ENSO (either the El
Nino or the La Nina phase) has been observed
for the southern Peru region (Minaya 1994;
Rome-Gaspaldy and Ronchail 1998). The very
strong 1982-1983 El Nino event was charac-
terized by intensified drought in Arequipa and
a strong deficit of the Majes River flow (17,058
km 2 watershed, 450 km long, spring at 4886 m
on the western flank of the Andean Cordillera),
but other strong El Nino events, such as the
1972-1973 event, were marked by exceptional
rainfall at Arequipa and maximum flows of the
Majes River (Minaya 1993, 1994) (Fig. 2).
These inconsistencies are linked to complex cli-
matic mechanisms operating in this particular
region involving a variable position of the In-
tertropical Convergence Zone, substantial dif-
ferences in the atmospheric circulation patterns
during different ENSO events, and interactions
between the coastal area and the cordilleran
zone.

Debris-Flow Episodes and Strong Rainfalls
in Southern Peru

In arid countries, debris-flow activity is tightly
linked to the occurrence of relatively intense
rainfalls. In the Chile-Peru coastal desert, de-
bris-flow activity may be observed with precip-
itation amounts above 20 or 30 mm, and after
rainfall episodes that last more than 3 hours
(Vargas et al. 2000).

The occurrence of heavy rainfall episodes,
debris flows, and inundations of the coastal re-
gion of Tacna (southern Peru) was compared
with available monthly rainfall data, informa-
tion obtained from local newspapers, and
ENSO indexes for the period 1960-2000. The
mean annual rainfall at Tacna for this period
was 19 mm. The total annual rainfall data and
the annual mean Southern Oscillation Index

(SOI) do not show any significant correlation.
However, a coincidence between years with an
excess of rainfall and low values of SOI (Fig.
3) was observed. On the other hand, not all the
years characterized by low SOI values exhibit
an annual excess of rainfall. Between 1960 and
2000, there were 1 1 "rainy" months (rainfall >
19 mm per month). Three of them (September
1960, September 1961, and September 1962,
with 20.2, 34.6, and 33.0 mm of total accu-
mulation, respectively) do not correlate with El
Nino events (as defined by Trenberth 1997). For
the rest of the cases (January 1983 and January
1998, with respectively 24.0 mm and 21.2 mm
total rainfall; July 1963 and July 1972, with re-
spectively 32.0 mm and 59.0 mm total rainfall;
September 1963, September 1965, and Septem-
ber 1997, with respectively 33.1, 22.6, and 31.7
mm total rainfall; and December 1997, with
28.2 mm of total rainfall), a correlation is ob-
served with El Nino events as defined by Tren-
berth (1997). During La Nina episodes, -an ex-
cess of precipitation events has not occurred.

Information published in local newspapers in
Tacna allows a historical reconstruction of the
heavy rainfall episodes and debris flows in this
region for the last 40 years (Table 1). In the 1 1
months with heavy rainfall previously men-
tioned, debris flows occurred in January 1983
and September 1997, and to a lesser extent in
July 1972 and January 1998. In these cases, the
heavy rainfall episodes occurred during El Nino
events of strong intensity, characterized by low
SOI values and important anomalies of the sea-
surface temperature at Puerto Chicama (Table
1, Fig. 4). The chronicles indicate a great spatial
variability in the total amount of precipitation
related to the strong convective character of the
storms. During these heavy rainfall events, as
was shown for the coast of northern Chile by
Vargas et al. (2000), the rain frequently oc-
curred at night.

A similar relationship between heavy rainfall,
debris flows, and El Nino events was deter-
mined for the coastal area of the Atacama des-
ert, and particularly at Antofagasta (23S), in
northern Chile (Vargas et al. 2000). In northern
Chile, not all El Nino events provoke "heavy"
rainfall episodes, but all the events able to pro-
duce debris flows (rain intensity > 20 mm/3
hours; Hauser 1997; Vargas et al. 2000) oc-
curred during the development phase of El Nino
events, in the austral winter (Rutllant and Fuen-
zalida 1991; Garreaud and Rutllant 1996). In

Debris-Flow Deposits and El Nino Impacts

Figure 2. Comparison of annual streamflow anomalies of Majes River (southern Peru) and variation in the
Southern Oscillation Index (SOI) during the 1950-1991 period (streamflow data from Corporation de la Aviaci6n
Civil, CORPAC, in Minaya 1994). No clear-cut correlation is observed between El Nino (negative SOI values) or
La Nina (positive SOI values) and the Majes River streamflow.

1925, 1930, 1940, 1982, 1987, and 1991, heavy
rainfall episodes in northern Chile were linked
to storms coming from mid-latitude regions.

In the coastal area of southern Peru, the cli-
matic mechanisms involved in the generation of
"heavy" rainfall events are not yet totally un-
derstood. While debris-flow events related to
heavy rainfall episodes were contemporary with
strong El Nino events (Fig. 4), some of them
occurred during the austral summer (January
1983 and January 1998), while others occurred
during the austral winter or spring (July 1972
and September 1997). The strong rainfall events
occurring in the coastal area during the austral
summer should be linked to the activity of the
rainy season on the Altiplano and the cordillera.
Those occurring in winter during El Nino years
are not clearly understood and cannot be readily
related to the same processes described in
northern Chile (frontal systems coming from
mid-latitude regions).

Because the reliable instrumental data cover
a relatively short time period, we investigated
the relationship between regional strong rain-
falls and ENSO during the last few centuries.

Historical Rainfall Data and

El Nino Manifestations During the

Last Four Centuries

Documentary data on climate in Peru and Chile
were largely used by Quinn et al. (1987), Quinn
and Neal (1992), Hocquenghem and Ortlieb
(1992), and Ortlieb (1999, 2000) to try to es-

tablish a sequence of El Nino events during the
last few centuries. Documentary sources consist
of reports on droughts, river flooding, the de-
struction of bridges and buildings, good and
poor crops, heavy storms, and other impacts of
meteorologic conditions. Information was ob-
tained from a variety of official, ecclesiastical,
and particular documents left by the Conquis-
tadores and the later inhabitants of these regions
during colonial times and after independence
from Spain. These data led to different inter-
pretations by the above-mentioned authors.
Whereas Quinn tended to interpret reports of
storms and heavier rainfall than usual along the
coastal desert of Peru or in central Chile as ev-
idence of past El Nino conditions, Ortlieb
(2000) considered that only information on pre-
cipitation excess in coastal northern Peru and in
central Chile could be reliably used as an El
Nino indicator. Hocquenghem and Ortlieb
(1992) and Ortlieb (2000) argued that, based on
instrumental records of the last decades, Rimac
River floods (in Lima) and unusual vegetation
cover along the coast of southern Peru should
not be taken by themselves as evidence of El
Nino conditions. Unusual vegetation growth in
the lomas (hilltops) in the area of Ilo could be
due to intensified winter garuas (coastal fogs),
not necessarily to strong rainfall. In some cases
it was shown that droughts in coastal northern
Peru were coeval with vegetated lomas in
southern Peru, probably during La Nina con-
ditions.

Previous work on documentary sources on
climate anomalies in the Norte Grande of Chile
showed that reliable data for the scarcely in-

L. Ortlieb and G. Vargas

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habited Atacama desert were for practical pur-
poses limited to the last two centuries (Ortlieb
1995). However, some additional and fragmen-
tary data from northernmost Chile and southern
Peru have recently turned up (Ortlieb 2000). Ta-
ble 2 presents data gathered on unusual rainfall
and debris-flow activity in the coastal areas of
southern Peru and (present-day) northernmost
Chile (north of 23S) since the earliest docu-
mentary record, dated 1619. Information on
heavy rainfalls in the central depression of
northern Chile, and floods in the quebradas
coming from the cordillera, which are linked to
La Nina conditions in the Altiplano and the An-
dean Cordillera, were not considered (unless
they co-occurred with precipitation anomalies
along the coast). The precipitation excesses are
compared with past occurrences of El Nino (or
La Nina) events as proposed by Quinn and Neal
(1992), Ortlieb (2000), and Ortlieb et al. (2002).
The last three columns of Table 2 do not con-
tain all the reconstructed El Nino (and La Nina)
events (according to the cited authors) but only
those that are contemporaneous with the hydro-
logic anomalies indicated in the first two col-
umns at left.

Table 2 shows that most heavy rainfall epi-
sodes and debris-flow activity registered in the
coastal study area occurred during El Nino
years, as determined by either one or all of the
cited authors. Several cases of flooding of the
San Jose or Azapa Rivers at Arica are not re-
lated to rainfall in the coastal area but reflect
precipitation excess in the Andean Cordillera,
during La Nina (or normal) conditions.

The historical data presented here cannot be
regarded as definitive, for several reasons. First,
documentary data are inherently fragmentary
and subject to error, exaggeration, and misin-
terpretation. Second, we still lack a reliable
chronological sequence of El Nino occurrences,
as evidenced by conflicting accounts in the last
three columns of Table 2. Third, the informa-
tion on river floods does not always show the
effects of cordilleran versus coastal rains. Rain-
fall in the upper part of the watersheds, in both
southern Peru and northern Chile, follows dif-
ferent regimes and has quite different mecha-
nisms from precipitation in the coastal areas.
Nevertheless, the historical data presented in
Table 2 tend to confirm that in a longer term
than the last few decades, precipitation excess
in the studied coastal area was generally ob-
served during El Nino years, and that El Nino

L. Ortlieb and G. Vargas

-1.5

to to to <o <o

Total annual rainfall at Tacna: 1960-2000

>^^v

!I
II

<u -a

S 2

Jan Mar May Jul Sep Nov
Mean monthly rainfall at Tacna: 1960-2000

Figure 3. A. Comparison of total annual rainfall at Tacna and SOI during the 1960-2000 period (monthly rainfall
data from SENAMHI, Peru). B. Distribution of the mean monthly rainfall at Tacna for the same period.

conditions do not systematically induce rainfall
excess in the study area.

During the last centuries, as during the last
decades, intense rainfalls and debris-flow activ-
ity often occurred during El Nino years, but the
relationship is not as tight as for the coast of
northern Peru. The "intense" rainfalls on the
coast of southern Peru are linked to convective
features, which may be favored by one or an-
other side effect of the anomalous patterns of
atmospheric circulation induced by ENSO in
the region.

near Punta El Ahogado, a sequence of debris-
flow deposits yielded a new radiocarbon data
set.

A comparison of the geomorphic contexts
and chronological data at these three localities
may provide insight into the geologic and pa-
leohydrologic processes during the Pleistocene-
Holocene boundary and in the first half of the
Holocene. The following discussion considers
to what extent the debris-flow units may be re-
lated to former occurrences of the El Nino phe-
nomenon.

The Latest Pleistocene/Early
Holocene Debris-Flow Episodes

Several localities on the coast of southern Peru
recently yielded new data on the age of late
Quaternary debris flows. Most of the radiocar-
bon data was obtained from material of an-
thropic origin: charcoal fragments, organic mat-
ter, and marine shells. One study (Keefer et al.
1998) has addressed the sequence of latest
Pleistocene early Holocene alluvial deposits on
the bank of the deeply incised Quebrada Taca-
huay, 40 km south of Ilo (see Fig. IB). In an-
other study, Fontugne et al. (1999) examined
the alluvial sequence at Quebrada Los Burros,
30 km to the south of Tacahuay. In between,

The Quebrada Tacahuay Sequence

Keefer et al. (1998) Data. In a locality south
of Ilo, on the northern bank of Quebrada Ta-
cahuay (1750'S, 7107'W), Keefer et al. (1998)
studied a geologic section atop an inland allu-
vial fan that encompasses the late Pleistocene-
mid-Holocene period. The section exposes 19
debris-flow and flood deposits, with the most
recent of them bearing remains of human oc-
cupation (including charcoal fragments, bird
bones, and a few marine shells) (Fig. 5). Keefer
et al. (1998) distinguished four periods in this
sequence:

Before an archaeological horizon at 12,700

Debris-Flow Deposits and El Nino Impacts

n 5

O -3 <

Figure 4. Total monthly rainfall at Tacna and sea-
surface temperature anomalies at Puerto Chicama for
periods with occurrence of debris-flow events or in-
undations along the coast of southern Peru.

5290 BP

8655 BP

9435 BP

>^ /10.560BP

\ 4 \10.895BP

( 12,490 BP
< 1 2.670 BP
* 12,730 BP

Debris flow

Sheetflood or channel flood

Aeolian

Midden

Occupation layer (aeolian

with water-laid silt)

Desiccation crack filled with
aeolian sand

Figure 5. Composite stratigraphic sequence of
the Quebrada Tacahuay. south of Ilo (from Keefer et
al. 1998). Ages are expressed in calibrated years (cal.
B.P.). Units Kl, K2, K3, K4cl, K4c2. K6, and K7 are
described as debris flows. Unit K8 is the main occu-
pation layer. Radiocarbon data from this sequence are
shown in Table 3.

cal. B.P., a sequence of eight debris-flow de-
posits, three aeolian sand layers, and two ma-
jor flood units. From an infrared-stimulated
thermoluminescent (TL) dating at 38.2 ka at
the base of this sequence, Keefer et al. (2001)
later inferred that these 10 debris-flow and
alluvial events occurred between 38,200 ka
and 12,700 cal. B.P.

Between 12,500 cal. B.P. and about 8800 cal.
B.P., four extensive debris-flow deposits were
formed (their units 2, 3, 6, and 7 [see Fig. 6],
which we will refer to here as K2, K3, K6,
and K7).

Between 8800 and 5300 cal. B.P., they rec-
ognized one debris-flow unit, which can be
subdivided into two thin layers (subunits
K4cl and K4c2, observed in a single profile)
overlying an aeolian sand unit (K4c3).
At ca. 5300 cal. B.P. (= 4550 60 B.P.) one
last major debris-flow deposit (unit Kl)
formed just before the main channel of Que-
brada Tacahuay began to be incised.

Presently, the floor of Quebrada Tacahuay

lies about 30 m below the top of the sedimen-
tary sequence. This sequence, cut by the paved
coastal road, is located about 1 km inland from
the shoreline.

In their study, Keefer et al. (1998) empha-
sized the archaeological aspects of their find-
ings. The major and oldest human occupation
was dated to 12,700-12,500 cal. B.P. and was
apparently interrupted because of the occur-
rence of a large debris flow (unit K7; see Fig.
5). The archaeological remains, including a
well-preserved hearth, which are found in a 10-
to 50-cm-thick layer of water-laid silt, with in-
terstratified lenses of aeolian fine sand (unit K8
in Fig. 5), are atypical because they include
very few marine shells, abundant seabird bones,
some remnants of pelagic fishes, and a few lith-
ic artifacts.

Our Data. During a brief visit to this locality
(in 1998), observation and sampling were con-
ducted in the southwestern part of the area stud-
ied by Keefer et al., to the west of the road.
Figures 6 and 7 show the studied sequence,

L. Ortlieb and G. Vargas

Debris-Flow Deposits and El Nino Impacts

L. Ortlieb and G. Vargas

with units numbered Tl to T6 from bottom to
top. The upper layer, designated T6 (equivalent
to unit Kl of Keefer et al. 1998) is a thick de-
bris-flow deposit that is colored dark by abun-
dant organic matter. Below it occur (from top
to bottom) a composite debris-flow deposit
(T5), an alluvial (sheet flood) unit (T4), another
debris-flow unit (T3), a composite alluvial layer
(T2), and a coarse fluvial conglomerate (Tl).
Radiocarbon data (Table 3) were obtained on
the two alluvial layers T2 and T4, both water-
laid deposits that incorporate a high amount of
reworked aeolian sand. Unit T4 contains char-
coal fragments, seemingly related to washed-
out hearths; marine shells brought by man; and
abundant terrestrial gastropods (not necessarily
linked to a human occupation). This unit T4
includes remnants of a relatively young phase
of human occupation dated to about 9000 cal.
B.P. and referred to as "the shell midden" by
Keefer et al. (1998). Unit T2, which is practi-
cally devoid of marine shells and contains many
bird bones, is the major "occupational" layer
of Keefer et al. (1998) that is, their unit K8.
Our chronological data and those of Keefer
et al. are presented in Table 3.

Paleohydrologic and Paleoclimatologic In-
terpretations. The Quebrada Tacahuay se-
quence thus consists in a succession of alluvial
and sheet flood units, debris-flow deposits, and
aeolian sand units. The water-laid sediments
can be separated in two categories: the alluvial
units, which were deposited in the bed (or the
banks) of the Tacahuay river, and the debris-
flow and sheet flood units, which are linked to
superficial runoff, not necessarily within the
valley. The dark brown (T6) or reddish (T5 and
T3) colors of the debris-flow units (Fig. 6) re-
sult from the proportions of clay, silt, and re-
worked soil in the matrix; the larger size com-
ponents may be subrounded to angular. The al-
luvial units are generally gray or yellowish;
their matrix is coarse-grained, and they include
pebbles and blocks of varying size, which may
be rounded to subangular. The sheet flood de-
posits generally consist of thin layers or lenses
of sands that show current figures, laminations,
cross-bedding structures, and the like. They
may include layers bearing reworked material
(shells, bones, charcoal fragments).

The petrographic composition and the shape
of the coarse elements found in the thickest al-
luvial units of the sequence clearly indicate that

the material comes from upstream in the rela-
tively large watershed of the Quebrada Taca-
huay. Because the watershed is of limited size,
there is no doubt that the hydrologic regime
was controlled by rainfalls in the coastal region.
The >25-m-thick sequence of (mainly) alluvial
deposits that predate the T1/K9 unit (Fig. 7)
corresponds to a late Pleistocene episode of ac-
tive, aggrading, sedimentation processes. It is
inferred that the hydrologic regime was con-
trolled by regular and abundant rainfalls. The
scarcity of chronological data from the Pleis-
tocene sequence (besides the 38.2 ky TL date
obtained by Keefer et al. 2001) hampers any
precise paleoclimatic and paleohydrologic in-
terpretation.

The debris-flow units are mainly formed
from superficial material eroded from the to-
pographic surface, including interfluves and
nearby hill slopes. The formation of these de-
posits implies that relatively strong and intense
rainfalls occurred in the immediate vicinity of
the outcrops. The debris-flow units have a lim-
ited lateral extension. As shown in Figure 7, the
debris-flow unit T6/K1 formerly extended on
both northern and southern sides of the present-
day thalweg of Quebrada Tacahuay. This ob-
servation provides a maximum age (5290 cal.
B.P.) for the beginning of the incision of the
quebrada at this locality. We surmise that the
downcutting of the thalweg responded more di-
rectly to retrogradation processes of the incision
related to the mid-Holocene high sea level than
to paleoclimatologic factors. Sometime around
5000 cal. B.P. linear erosion took over the up-
ward aggradation processes, at this locality rel-
atively close to the coastline. We interpret that
it was not precisely because of a variation in
the hydrologic regime that the thalweg was
formed and progressively entrenched. This is
not easy to demonstrate because the erosive
processes dominated during the second half of
the Holocene, and thus no subsequent sedimen-
tary deposit was preserved in this locality. In
other words, the morphologic evolution of the
locality during the late Holocene prevents us
from making any comparisons between present
(or recent) hydrologic conditions and those that
existed prior to the mid-Holocene.

Keefer et al. (1998) interpreted as evidence
for El Nino manifestations the half-dozen epi-
sodes of debris-flow events (units K7 to Kl,
Fig. 5) identified between 12,500 and 5300 cal.
B.P. They further suggested that, because of the

Debris-Flow Deposits and El Nino Impacts

Quebrada El Canon

Holocene eolian sand

Late Pleistocene aljuvial sequence

~S" JtSK 1 ,

Figure 8. Late Pleistocene coarse alluvial units overlain by an early Holocene sandy layer and by a late Holocene
occupational horizon (sand and silts with abundant charcoal and ceramic fragments) in Quebrada El Canon, about 1
km south of Quebrada Los Burros, southern Peru. The Pleistocene alluvial units are most probably coeval with those
of Quebrada Tacahuay and with the oldest debris-flow deposits of Punta El Ahogado.

sedimentologic similarity between these debris-
flow deposits and those that predate unit K8
(i.e., older than 12,700 cal. B.P.) in the sequence
of Quebrada Tacahuay, El Nino conditions were
also present during the late Pleistocene. These
interpretations are essentially based on the as-
sumption that, as at present, violent rainfalls in
this coastal area would characteristically have
occurred during El Nino years.

We disagree with the interpretations of Kee-
fer et al. regarding the character of ENSO prox-
ies of the debris-flow units. Too little is known
about the morphoclimatic and paleohydrologic
local conditions at the end of the Pleistocene in
the Tacahuay region, and more generally in
coastal southern Peru. The superposition of
sheet flood, debris-flow, and alluvial sediments
has no modern equivalent and does not repre-
sent climatic conditions comparable to present
conditions. Instead, the abundance of alluvial
layers for the late Pleistocene part of the Ta-
cahuay sequence suggests a more humid cli-
mate, with stronger and more regular flow ep-
isodes, than in the late Holocene. If this was the

case, there is no reason to infer that debris-flow
activity was linked to El Nino conditions.

Quebrada Los Burros Area

Fontugne et al. (1999) also addressed the prob-
lem of the local impact of El Nino during the
Holocene. Their study was performed in the
framework of another archaeological project
centered on Quebrada Los Burros, an early Ho-
locene site located some 40 km south of Taca-
huay (see Fig. IB) (Lavallee et al. 1999). Ac-
cording to Fontugne et al. (1999), two major
debris-flow deposits (huaycos) were formed in
Quebrada Los Burros: the oldest one occurred
around 8980 cal. B.P. (between QLB2: 8160
70 B.P. and QLB3: 8040 105 B.P., conven-
tional ages), and the youngest one was dated to
slightly after 3380 cal. B.P. (see Table 3). Be-
tween these two units, ten layers of organic
matter and pseudo-peat accumulations were in-
terstratified (Fig. 8). These layers were inter-
preted by Fontugne et al. (1999) as representing

L. Ortlieb and G. Vargas

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L. Ortlieb and G. Vargas

more humid spells, with a typical duration of
less than 200 years. Such episodes of "in-
creased soil moisture" would have been linked
to reinforcements of winter fogs and enhance-
ments of the coastal upwelling strength. Fon-
tugne et al. thus infer that no El Nino would
have occurred between 8970 and 3380 cal. B.P.

It must be noted that after 3380 cal. B.P., no
other debris-flow deposit was recorded in Los
Burros valley.

In this case, as at Tacahuay, the previous au-
thors suggest that debris-flow activity is typical
of El Nino conditions, to the point that lack of
a debris-flow deposit would imply that no El
Nino event occurred. Again, we disagree with
this interpretation.

Quebrada Los Burros is a small drainage sys-
tem surrounded by bare bedrock, particularly in
the lower part of the valley. There is scarce su-
perficial soil material susceptible to be re-
worked by runoff during violent rainfalls.
Therefore, we consider that the lack of debris-
flow deposit during a given time period should
not be interpreted as an indication of absence
of intense rainfall. This view is supported by
the fact that a strong local rainfall in mid-Sep-
tember 1997 (see Table 1), during an El Nino
year, did not generate a characteristic deposit in
Quebrada Los Burros, although it produced a
debris-flow event less than 2 km to the south,
in the small Quebrada El Canon.

The formation of two debris-flow deposits in
Quebrada Los Burros reflected the occurrence
of strong rainfalls in the valley, but it still re-
mains to establish that the rainfalls were related
to El Nino conditions. The organic-rich layers
interstratified between the two debris-flow units
indicate that humid conditions persisted for
some time in the valley, but these conditions
might have been related to a natural (or possi-
bly man-made) dam downstream, in the valley.
Such a feature, which can be inferred from the
remnants of tuffa and carbonate concretions
stuck to the bedrock, may have maintained an
artificially high base level within a portion of
the valley. Hence, the existence of pseudo-peat
deposits in the center of the thalweg may not
be directly linked to paleoclimatologic factors.

The sedimentary histories of Quebrada Ta-
cahuay and Quebrada Los Burros show little
correspondence. The oldest debris-flow unit of
the latter seems to have been almost contem-
poraneous with the K2 unit of the former (see
Table 2).

In Quebrada El Canon, immediately to the
south of Quebrada Los Burros (see Fig. IB), a
complex sedimentary sequence is found that
begins with a thick series of coarse alluvial de-
posits and resembles the Pleistocene part of the
Tacahuay sequence (Fig. 8). In Quebrada El
Canon at least a dozen superposed alluvial units
of comparable thickness (about 20 cm each)
suggest a vigorous alluvial activity of this river,
comparable to that of Quebrada Tacahuay. No
radiocarbon date has yet been obtained for this
series, but the alluvial sequence can be assigned
to the Pleistocene because it underlies a major
unit of aeolian sand containing human bones
dated to 9830 140 B.P. (uncalibrated) (Fon-
tugne and Lavallee, pers. comm., 1999). It is
interesting to note that a similar phase of aeo-
lian sand deposition (involving enhanced wind
activity) also occurred near the Pleistocene-Ho-
locene transition in the Antofagasta area, 700
km to the south (Llagostera 1979; Vargas 1996;
Vargas and Ortlieb 1998).

The informal name of "El Canon" was given
to this quebrada because of a deep incision cut
into the >50-m-thick sand dune that was built
up along the coastline at that time, and which
obstructed the mouth of the river. The "canon"
is thus the result of the erosive action of the
strongest floods that occurred in the Holocene.
The last time that a flood flowed through the
canon was during the 1997-1998 El Nino event.

El Ahogado Sequence

The El Ahogado sequence of debris-flow de-
posits, which is located halfway between Que-
brada Tacahuay and Quebrada Los Burros, was
revisited recently (after a preliminary study in
1990). This sequence, observed in a roadcut
(Fig. 9), lies on an interfluve between two small
quebradas at the foot of the 600-m-high coastal
range. It consists of a succession of at least 15
debris-flow units. These units, which are 10 to
30 cm thick, can be described as mud flows that
incorporate unsorted material from upslope
floating in a silty matrix. The reworked clasts
are angular to subrounded, ranging in size from
a few millimeters to 50 cm in diameter. The
sedimentologic characteristics of the deposits
clearly indicate that they resulted from mass
flow of limited energy that reworked superficial
clasts from the alluvial fans accumulated at the
foot of the nearby range. They were formed

Debris-Flow Deposits and El Nino Impacts

during strong rainfall episodes that struck the
coastal region proper, which, in the area, ex-
tends only some 3 or 4 km between the range
itself and the coastline.

A particularity of this locality is that a few
debris-flow units overlie remnants of anthropic
activity that can provide radiocarbon dates, and
thus the maximum ages of the respective geo-
logic deposits. The third youngest debris-flow
unit overlies a layer with abundant marine
shells, bird remains, terrestrial mollusks, rope
fragments, and charcoal. Three charcoal frag-
ments from this horizon yielded calibrated ages
of ca. 3764, 3780, and 3946 cal. B.P. (Table 3).
We can therefore infer that the deposit was
formed sometime after 3760 cal. B.P. Similarly,
the fourth youngest unit overlies a relatively
thin, sandy layer that includes a few anthropic
remains and many bird remains; charcoal frag-
ments from this horizon yielded a date of 7573
cal. B.P. (Table 3). The maximum age of this
penultimate debris-flow deposit can thus be es-
timated to be around 7570 cal. B.P.

This last finding suggests that at least one
other debris-flow episode occurred between the
two events dated at Quebrada Los Burros (3380
and 8970 cal. B.P.; Table 3). The 14 C date ob-
tained on the youngest anthropic layer does not
preclude that the youngest debris flow of Punta
El Ahogado (<3760 cal. B.P.) was contempo-
raneous with the youngest one identified at
Quebrada Los Burros (ca. 3380 cal. B.P.). No
geochronological data are available from the
older debris flows in the El Ahogado sequence.

One other observation, made in a comparable
sequence located 600 km to the north of this
locality, provides useful information. In a road-
cut located at km 737 of the Panamerican High-
way, 40 km north of Ocona, at Playa Muerta
(see Fig. 1A), anthropic remains with charcoal
fragments dated to 9130 and 9006 cal. B.P. (Ta-
ble 3) were found below the fourth youngest
debris-flow units (Fig. 10). Because of the sim-
ilarity of the geomorphic situation of the El
Ahogado and Playa Muerta debris-flow se-
quences, we surmise that the two last-formed
units in each locality were coeval. The oldest
debris-flow units observed at El Ahogado are
probably of Pleistocene age.

Because of its morphologic location, on an
interfluve, the El Ahogado sequence cannot
provide a record of latest Holocene debris-flow
activity. The small quebrada located immedi-
ately to the south of the locality attracted most

L. Ortlieb and G. Vargas

'.'; V 1 "-

m 737 Panamerican Hwy.

Figure 10. Alluvial sequence of debris-flow deposits at Playa Muerta, southern Peru.

of the debris-flow sediments in the course of
the last few millennia.

Regional Correlation of Debris- Flow
Remnants

The geochronological data from the four local-
ities Quebrada Los Burros, Quebrada Taca-
huay, Punta El Ahogado, and Playa Muerta
in the southern Peru coastal region suggest that
some of the alluvial and debris-flow units may
be contemporaneous. Table 4 recapitulates the
available data and shows a tentative lateral cor-
relation between the four sequences.

The latest Holocene debris-flow episode ob-
served in Quebrada Los Burros and the third
youngest unit at El Ahogado are younger than
3380 cal. B.P. The previous dated event, youn-
ger than 5290 cal. B.P., was identified in Que-
brada Tacahuay, and may have been preserved
at El Ahogado as well. An older event, appar-
ently of strong intensity, might be represented
in three localities (Playa Muerta, Tacahuay, and
El Ahogado) and can be dated to ca. 8660 cal.

B.P. The previous ones were all dated in the
Quebrada Tacahuay locality and would have oc-
curred around 9440, before 10,560, before
10,920, at some time between 10,920 and
12,490, and before 12,490 cal. B.P. The locali-
ties of Tacahuay, El Ahogado, and El Canon
recorded a series of at least 15 alluvial events
before 12,500 cal. B.P.

Discussion

Debris-Flow Significance in Northern Chile
and Southern Peru

The extreme aridity of the coastal area of south-
ern Peru favored the formation and subsequent
preservation of debris-flow deposits. The narrow
coastal plain at the foot of several high rocky
mountain ranges, the general lack of soil cover,
the abundance of hill-slope material available for
transport, and the episodic character of extreme-
ly rare rainfall events all contributed to debris-
flow activity in this region. Sequences of piled-
up debris-flow deposits in areas at the foot of

Debris-Flow Deposits and El Nino Impacts

steep alluvial fans or near small quebradas are
a particularity of the coastal region of southern
Peru and northern Chile. Thick sequences of
such deposits were studied in the Antofagasta
area (23S), in northern Chile (Vargas 1996; Var-
gas and Ortlieb 1998). It was shown there that
the hydrologic and meteorologic conditions al-
lowing debris-flow activity were set up during
the middle Holocene (around 5600 cal. B.P.) and
that no debris-flow deposition seems to have oc-
curred in the early Holocene (Vargas et al. 2000;
Vargas 2002). Available information on late
Pleistocene sedimentary deposits in the Antofa-
gasta region suggests that moderate and possibly
regular rains, unable to provoke debris-flow de-
posits (like those produced under present-day
conditions), fell during the Late Glacial Maxi-
mum (Vargas 1996; Vargas and Ortlieb 1998).
The Pleistocene-Holocene transition was
marked in the bay of Antofagasta by the accu-
mulation of an aeolian sand sheet that shows
strong wind activity.

Along the southernmost coast of Peru, the
geologic record of the late Quaternary suggests
a different story than the paleohydrologic re-
construction proposed for the Antofagasta re-
gion. We saw that in southern Peru, debris-flow
units were formed in the late Pleistocene, the
Pleistocene Holocene transition, and the early
Holocene. The record of debris-flow activity
during the second half of the Holocene is lim-
ited, in contrast to the existence of relatively
thick sequences of debris-flow units found in
some localities of the Antofagasta area. These
differences are interesting and lead us to pro-
pose new interpretations regarding the mecha-
nisms involved in the formation of debris-flow
deposits and their causal relationship with
ENSO conditions in both regions.

In the coastal area of northern Chile, the oc-
currences of strong rainfall events, able to pro-
duce debris-flow activity, are clearly linked to
a combination of ENSO conditions and addi-
tional favorable circumstances (Garreaud and
Rutlland 1996; Vargas et al. 2000). In fact, all
of the rainy events with a minimum amount of
20 mm of rainfall that were recorded in the
twentieth century in Antofagasta area occurred
during El Nino years, while winter precipitation
excesses were recorded in central Chile. How-
ever, this relationship is conditioned by various
other factors that control a northward shift of
frontal systems and the spatial distribution of
convective activity. During some El Nino years

(even of strong intensity), it does not rain in
northern Chile.

In southern Peru, we showed that, at least at
present, the relationship is much weaker be-
tween strong rainfall episodes and ENSO con-
ditions. First, a distinction must be made be-
tween the coastal region and the area close to
the cordillera. El Nino events are generally
characterized by drought in the Altiplano and
the Andean areas, while rainy episodes may or
may not occur near the coast. As in northern
Chile, the convective character of the rains may
explain the apparently erratic location of the de-
bris-flow activity, when it is observed. By ex-
amining both the instrumental record and his-
torical documentary data, we found that El
Nino years are not characterized by precipita-
tion excess (even in the coastal area). This is
one difference from the situation observed in
northern Chile. Another difference is that heavy
rainfall episodes in coastal southern Peru may
occur in different seasons. This observation
suggests that different regional mechanisms
may be involved, some of them possibly unre-
lated to ENSO conditions. However, it does ap-
pear that most debris-flow episodes in southern
Peru over the past two centuries occurred dur-
ing El Nino events.

Before we address the question of the rela-
tionship between late Pleistocene and early Ho-
locene debris-flow activity and ENSO condi-
tions, it may be useful to discuss how the geo-
chronological framework for these kinds of de-
posits was determined.

Dating Debris-Flow Activity

The scarcity of organic matter, plant remains, or
material that can be dated within the debris-flow
units generally hampers their direct age deter-
mination. In only a few cases has it been ob-
served that some mud flow overlaid or reworked
charcoal remains and other remnants of human
activity (shells, bones). In these cases, the radio-
carbon age of the dated material provided a max-
imum age for the debris-flow activity. In this
study, we mentioned only geochronological data
obtained on terrestrial material (plants, charcoal,
and organic matter) and avoided data based on
marine shells or bones of marine mammals.
Large uncertainties about the reservoir effects,
which may have varied over time in a region
subject to various upwelling phenomena (Taylor

L. Ortlieb and G. Vargas

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Debris-Flow Deposits and El Nino Impacts

and Berger 1967; Stuiver and Brazunias 1993;
Southon et al. 1995), weigh upon radiocarbon
results obtained on carbonates of marine origin.
As Kennett et al. (2002) showed in a study based
on a comparison of marine and terrestrial mate-
rial from the Ilo region, it is not yet possible to
determine whether the reservoir effect varied
significantly since the late Pleistocene in this re-
gion. The strong aridity so drastically limited the
availability of fuel wood that the charcoal re-
mains of archaeological sites may predate by
several centuries the time of their ignition, thus
impeding any calibration study between shells
and charcoals.

The radiocarbon ages measured on charcoal
remains underlying debris-flow deposit are nec-
essarily older than the rainfall episode that pro-
voked the flow. But since the wood used for
fire may have been burned several centuries af-
ter the death of the tree, the apparent date of
the charcoal may be significantly older than
measured. These uncertainties must be kept in
mind in the proposed comparison between max-
imum ages of the debris-flow activity in the dif-
ferent studied localities (Tables 3 and 4). How-
ever, in spite of these unavoidable sources of
unaccuracy, the general chronological frame-
work proposed in Table 4 seems acceptable.

Some of the dates measured on organic ma-
terial (not charcoal) or roots within sedimentary
units of the sequences at Quebrada Tacahuay
and Los Burros by earlier authors may be more
reliable because their contemporaneity with the
deposits is better assessed. Two of this kind of
radiocarbon result obtained in each quebrada
(ca. 8660 and ca. 8970 cal. B.P.) compare rea-
sonably well with the result obtained on the
charcoal remains at a third locality (Playa
Muerta, <9000 cal. B.P.) (Table 4). This obser-
vation brings some confidence to the lateral cor-
relation proposed here between the debris-flow
remnants across the region.

The stratigraphic disposition of the debris-flow
units studied here, combined with the available
geochronological data, thus indicate that a few ep-
isodes of strong rainfall occurred before and im-
mediately after the Pleistocene-Holocene bound-
ary. It is inferred that violent rainfalls probably
characterized this transition period.

Because of the entrenchment of the hydro-
graphic network starting in the middle Holo-
cene, it is difficult to compare the frequency of
occurrence of debris-flow activity throughout
the Holocene. Once quebradas were subjected

to vertical erosion, debris-flow deposits were
less likely to be preserved on the interfluves,
nor could they be recorded within the valleys.
As a result, the limited number of late Holocene
debris-flow units may be underestimated. Even
with this restriction in mind, it seems clear that
the debris-flow activity did not increase during
the Holocene quite the contrary. In the local-
ities visited in southern Peru, only one (or two)
debris-flow deposits formed in the last thousand
years was preserved, in sharp contrast to the
tens of units recorded in Antofagasta Bay. The
scarcity of recent debris-flow activity in the
study area of southern Peru does not suggest a
close relationship between ENSO conditions
(known to have occurred with high frequency
in the last few centuries) and the occurrence of
strong rainfall events.

Evidence for El Nino Conditions in the
Latest Pleistocene-Early Holocene

The occurrence of El Nino events and their char-
acteristics (frequency, intensity) during the Early
Holocene and at the end of the late Pleistocene
is a much debated question (DeVries et al. 1997;
Markgraf 1998; Sandweiss et al. 1999; Rodbell
et al. 1999; Andrus et al. 2002; Bearez et al.
2003). Keefer et al. (1998, 2001) developed the
hypothesis that the presence of debris-flow de-
posits along the coast of southern Peru consti-
tuted evidence for El Nino conditions since be-
fore the Late Glacial Maximum up to the pres-
ent. On the other hand, Fontugne et al. (1999)
argued that the lack of debris-flow units between
8970 and 3380 cal. B.P. in Quebrada Los Burros
could be interpreted as evidence for the lack of
El Nino conditions between these two dates.

In the case of Quebrada Los Burros, it can
be objected that lack of a debris-flow record
may be due to local geomorphic or hydrologic
conditions and does not constitute a strong ar-
gument against the occurrence of El Nino
events. Anyway, debris-flow units from nearby
localities (El Ahogado and Quebrada Tacahuay)
provide evidence for the occurrence of local
strong rainfall events in the middle Holocene
and later.

In Quebrada Tacahuay, debris-flow units and
alluvial sediments interstratified in a thick sed-
imentary sequence that encompasses the late
Pleistocene and the first half of the Holocene
suggest that the hydrologic conditions were

L. Ortlieb and G. Vargas

quite different than at present. A thick alluvial
sequence observed in Quebrada El Canon (Fig.
8) supports the hypothesis that a high runoff
existed at the end of the Pleistocene in the re-
gion. A much wetter climate, with respect to
the present-day situation, may thus have char-
acterized the area between at least 13,000 cal.
B.P. (or the Late Glacial Maximum?) and ca.
9000 cal. B.P. If, as we suspect, this was true,
then there is no reason to extrapolate the current
(weak) relationship between ENSO and strong
rainfalls. Local, relatively strong rainfalls may
completely explain episodic debris-flow activity
and the coarse alluvial deposits in several lo-
calities of coastal southern Peru.

Hence, we conclude that in coastal southern
Peru, debris-flow activity is not straightfor-
wardly related to ENSO conditions, even if in-
strumental data for the last decades and docu-
mentary historic data tend to suggest that some
weak relationship may have existed recently.
For more remote periods, during the postglacial
late Pleistocene and early Holocene, the cli-
matologic regime was quite different than at
present. Until better knowledge of this regime
is obtained, we believe it is misleading to infer
a causal relationship between debris flow and
ENSO in southern Peru for periods prior to the
middle Pleistocene.

Acknowledgments. This work was supported
by the program Paleoclimatologie et Variabilite
Climatique Tropicale (UR1), later replaced by
the program Paleoenvironnements Tropicaux et
Variabilite Climatique (PALEOTROPIQUE) of
IRD. Fieldwork (November 1998) was aided by
funding from the project Sud Perou (leader, D.
Lavallee) within the program Paleoenvironne-
ments et Evolution des Hominides (CNRS).
Previous fieldwork was done while the senior
author (and J. Machare) led a cooperative re-
search project between ORSTOM (now IRD)
and the Institute Geoffsico del Peru (1987-
1991). G. Vargas (University of Chile) benefit-
ed from an IRD scholarship while completing
a doctoral thesis at the University of Bordeaux.
We thank J. F. Saliege (LODYC, Universite de
Paris-CNRS-IRD) for radiocarbon data on the
localities of Tacahuay and El Ahogado, and J.
Rutllant (University of Chile) for his useful
comments on regional climate anomalies. We
also thank Wilber Chambi (Universidad Jorge
Basadre Grohmann, Tacna) for his help in com-

piling newspaper-published regional data, and
N. Guzman for her help in the field.

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Paleoenvironment at Almejas:

Early Exploitation of Estuarine Fauna

on the North Coast of Peru

Shelia Pozorski and Thomas Pozorski

The preceramic site of Almejas, with radiocar-
bon dates averaging about 5000 B.C.,' is among
the earliest marine-oriented sites in the Casma
Valley of Peru. The site consists of a dense shell
midden over 1 m deep that is unusual because
of the predominance of warm-water mud-flat
mollusks among the remains. Along with these
mollusks, an abundance of estuarine fishes in-
dicates a very rich estuarine ecosystem close to
the site. A single, well-preserved burial was also
encountered within the shell midden. The collec-
tive data from Almejas provide information
about early coastal settlement that is pertinent to
critical, much-debated issues regarding the tim-
ing of current sea level attainment and the antiq-
uity of the present climatic regime, including pe-
riodic El Nino-related events.

(Fig. 1). The site lies along the north side of a
granite outcrop against which considerable gra-
nitic sand is banked. Almejas is now about 5.5
km from the Pacific Ocean and about 25 m
above sea level, but the intervening area is quite
low, less than 5 m above sea level (masl), and
was once a large shallow estuary (Fig. 1).

In the immediate vicinity of the site are abun-
dant remains of much later Early Intermediate
Period and Late Intermediate Period (200 B.C.
to A.D. 1470) settlement, including a large cem-
etery, cane foundations of quincha (wattle-and-
daub) houses, and rich midden with abundant
plant remains. Slightly further north, in a nat-
ural basin also formed by low granitic hills, lies
the Early Horizon site of San Diego (Pozorski
and Pozorski 1987:51-65; Tello 1956:296-298;
Thompson 1961:74-75, 241-244, 1964:208).

The Site of Almejas

Location and Surface Features

A tiny preceramic site located near the aban-
doned hacienda San Diego was named Almejas,
a Spanish word meaning clam, because of the
abundant bivalve shells found on the surface

1 The 5000 B.C. date is based on uncalibrated radio-
carbon dates. If calibrated dates were used, then the
date for the site would be about 5900 B.C. However,
for the purposes of this discussion, uncalibrated dates
are used because the dates cited here for comparative
purposes have been reported in the archaeological lit-
erature as uncalibrated dates.

Excavations at Almejas

Almejas is distinguishable on the surface as an
irregular patch of very dense shell about 95 m
north-south by 50 m east-west. Excavation of
four test pits within the area of dense shell re-
vealed that this shell extends to a depth of 135
cm. A 1-m 2 controlled stratigraphic excavation
of the test pit exposed the deepest and best-
preserved midden deposit. Portions of the upper
levels had been disturbed and contaminated by
the activities of later inhabitants. These mixed
zones, which occasionally penetrated to a depth
of 40 cm, were easily detected, both because of
the extremely weathered condition of the early

Paleoenvironment at Almejas

2km

Pacific
Ocean

Figure 1. Map of the lower Casma Valley showing the location of the site of Almejas.

S. Pozorski and T. Pozorski

Figure 2. View from above showing three large boulders on top of the Almejas burial.

shell and because of the presence of intrusive
late elements such as ceramics, camelid dung,
and maize. The lower levels, however, were un-
disturbed and contained predominantly marine
shell, fish bone, and wild plant remains. A buri-
al was discovered within these intact lower lev-
els.

As the controlled stratigraphic excavation
was carried out, excavation followed the visible
stratigraphy. Thick levels were arbitrarily sub-
divided into artificial levels 25 cm or less in
thickness. Initial excavation of each level in-
volved the removal of a 25-cm 2 column sample
of midden that was screened through succes-
sively smaller mesh: l /4 in. screen, a no. 10 geo-
logical sieve, and a no. 25 geological sieve. The
remaining material from the more general ex-
cavation of each level was screened through a
V* in. screen. The plant and animal remains re-
covered when the column sample was screened
through the % in. mesh were included as part
of the general excavation material. Remains re-
covered using the geological sieves were
bagged separately according to mesh size. The
animal bone recovered using the geological
sieves was analyzed separately, but the results
have been combined here under the term "col-

umn sample." Volume measurements in liters
were recorded for all excavation units within
the stratigraphic cut.

Burial

A preceramic burial was encountered near the
bottom of the stratigraphic excavation at a
depth of 100 cm below the modern ground sur-
face (Figs. 2 through 4). The first clue that a
burial was present was three large boulders that
lay on top of the burial wrapping (Fig. 2). This
burial wrapping consisted of a well-preserved
covering of parallel junco reeds (Cyperus sp.)
laid lengthwise and closely spaced to cover the
body (Fig. 3), but without any evidence of twin-
ing or tying.

The body (Fig. 4) was tightly flexed, lying
on the right side with the head toward the north.
The arms were flexed, bringing both hands into
position beneath the chin. Based on examina-
tion of the pelvis, the skeleton was determined
to be that of a male. Formulae for stature cal-
culations developed by Genoves (1967; repro-
duced in Bass 1987:29) indicate that the man's
stature when alive would have been approxi-

Paleoenvironment at Almejas

Figure 3. View from above of the Almejas burial after removal of the three large boulders. Well-preserved loose
junco (Cyperus sp.) fibers covered the exterior of the body.

mately 161.5 cm. His age at death is estimated
at approximately 35 to 45 years. This age de-
termination is based on complete closure of all
epiphyses (Bass 1987:13-19), slight arthritic
lipping on the cervical vertebrae (Bass 1987:
19), and tooth wear as measured against the
scale developed by Brothwell (1981:72). All
four third molars, the lower second premolars,
and both lower right incisors were lost well be-
fore death; their corresponding sockets are no
longer visible. The remaining teeth are very
worn, exposing the dentine. Both ears contain
bony growths known as auditory exostoses; the
condition is particularly severe in the left ear.
These commonly result from trauma to the ear
canal when the thin skin there is exposed to
cold water while an individual is exploiting
cold-water resources (Kennedy 1986; Quilter
1989:21; Tattersall 1985:60-64; Wise et al.
1994:217).

A large quartz crystal (Figs. 4 and 5) was
discovered near the left hand, where it may
have been held. This item is unique in such a
context; and, given the frequent inclusion of
quartz crystals among power objects on the me-
sas of modern shamans practicing on the Pe-

ruvian north coast (Joralemon and Sharon 1993:
20, 32, 54, 68, 80, 95, 107), the quartz crystal
from Almejas may also have served prehistor-
ically as a power object for communicating
with and influencing the supernatural. This find
represents the earliest such evidence of possible
shamanistic practices along the entire central
Andean coast.

A total of 52 perforated shell discs were also
collected from the grave fill between the junco
wrapping and the center portion of the body
(Fig. 5). These were likely strung as beads, pos-
sibly once forming a necklace. Most of the shell
discs were manufactured from Trachycardium
procerum and Argopecten purpuratum shells,
although a few may have been fashioned from
the mussel Mytella guyanensis and the gastro-
pod Thais chocolata. Shell beads and worked
or cut shell ornaments have been found in some
burials at Late Preceramic sites (Bird and Hys-
lop 1985:66, 220; Feldman 1980:114, 121;
Moseley 1992:1 16; Quilter 1 989:53-74 passim;
Wendt 1976:34) and earlier preceramic sites
(Stothert 1985:627).

Other than the quartz crystal and shell discs
associated with the burial, very few artifacts

S. Pozorski and T. Pozorski

Figure 4. View from above of the excavated male skeleton at Almejas. The individual was 35 to 45 years old
at the time of death and was buried with 52 perforated shell discs, which likely once formed a necklace, and a large
quartz crystal, which he held in his left hand.

Figure 5. Perforated shell discs and the large quartz crystal found with the Almejas burial.

Paleoenvironment at Almejas

TABLE 1. Radiocarbon dates from Almejas.

Sample no.

Radiocarbon
years* B.C.

B.C.

equivalents

Calibrated
datet

Material

Context

UGa-4518

7195

5245

5980

130

Charcoal

Stratigraphic cut, level 4c,
80 cm below surface

UGa-4519

7220

5270

6000

120

Charcoal

Stratigraphic cut, level 4e,
100 cm below surface

UGa-4539

6875

105

4925

105

5675

180

Junco

From burial fiber wrapping,
burial cut into level 4e

* All dates are based on the Libby half-life (5568 30 years) and have no "C/ I2 C corrections.
t Calibrations are based on charts in Stuiver and Becker (1993).

were encountered at Almejas. These additional
artifacts include rounded shell discs and perfo-
rated pieces of shell that may represent partially
shaped perforated shell discs or beads.

The burial at Almejas is one of the earliest
preceramic burials that have been found along
the central Andean coast. Dating to approxi-
mately 5000 B.C., this burial predates all burials
associated with the Late Preceramic Period or
the Cotton Preceramic Period (3000-1800 B.C.),
a time period associated with the use of twined
cotton textiles for clothing, burial wrappings,
and netting (Bird and Hyslop 1985:64-76; Lan-
ning 1967:61: Moseley 1983:208, 1992:108-
109). A few widely scattered coastal sites have
yielded burials of comparable age: the earliest
burials at La Paloma on the central Peruvian
coast (Quilter 1989:11, 163-165), the burials
associated with the Late Las Vegas phase at the
Las Vegas in southern Ecuador (Stothert 1985:
618-619), and those of the Chinchorro Culture
in northern Chile and the far south coast of Peru
(Arriaza 1995:127-130). Somewhat earlier
burials (6000-8000 B.C.) have been found with-
in the Chinchorro culture sites (Arriaza 1995:
126-127), at Encampment 96 of Paracas Bay
(Arriaza 1995:55; Engel 1981:31-32; Quilter
1989:71), at the Paijan culture sites of Quiri-
huac Shelter in the Moche Valley (Chauchat
1988:49-51; Moseley 1992:87), and in the
Cupisnique desert north of the Chicama Valley
(Chauchat 1978b:60, 1988:59-63).

The Almejas burial has several traits typical
of and other traits not so characteristic of pre-
ceramic burials along the central Andean coast.
The body itself was buried in its natural state
with no attempt at artificial mummification.
With the exception of the unique Chinchorro
Culture (Arriaza 1995), this was standard treat-
ment for all preceramic burials along the coast.
The flexed position of the Almejas body, lying

on one side, is typical of many preceramic sites,
including those contemporary with, earlier than,
and later than the Almejas burial (Bird and
Hyslop 1985:64-76; Engel 1981:32-38; Feld-
man 1980:114-122; Grieder et al. 1988:Table
4; Moseley 1992:116; Pozorski and Pozorski
1979:351-354, 1987:20; Quilter 1989:53;
Stothert 1985:625; Wendt 1976:29-30; Wise et
al. 1994:215). The presence of large stones on
top of the Almejas burial is also a trait shared
with burials at several preceramic sites (Bird
and Hyslop 1985:66; Pozorski and Pozorski
1979:353, 1987:20: Quilter 1989:83; Stothert
1985:625; Wendt 1976:30). The wrapping of
bodies was a widespread practice in preceramic
times. In Late Preceramic times, cotton cloth
was most frequently used (Bird and Hyslop
1985:64-76; Feldman 1980:114-122; Moseley
1992:1 16); also common was the use of twined
or woven matting (Bird and Hyslop 1985:66-
74; Engel 1976:97, 1981:32-38; Feldman 1980:
114-118; Fung Pineda 1988:95; Quilter 1989:
53, 70-82; Wendt 1976:30-31). The use of
loose junco fibers, totora reeds, or other loose
plant fiber as a burial wrapping was less com-
mon (Bird and Hyslop 1985:74; Pozorski and
Pozorski 1987:20; Quilter 1989:87-162).

Subsistence and Environment

Two features of Almejas distinguish the site
from other preceramic sites of the central and
north coast. First, the radiocarbon dates for the
site, averaging about 5000 B.C. (Table 1), are
unusually early. Second, the predominant fau-
nal remains argue for a nutrient-rich estuary in
the vicinity of the site. The molluscan inventory
is dominated by species that disappeared from
the Casma area quite early and are now largely

S. Pozorski and T. Pozorski

Percentage of Shellfish Species Based on MNI

KV^

Level

1b
2a
2b
3a
3b
4a
4b
4c
4d
4e
5

Figure 6.

Individuals).

Y777A WA

Y/////////////A

X//////////7777A

Y/////////////A

Y/////////777A

V///////A
V///////X

VTA

I I

I I
I I

V///7//A

Y////////S77\

Y///////A

Diagram of shellfish species frequency through time at Almejas, based on MNI (Minimum Number of
Level 5 is the earliest level; level la is the latest.

confined to mud-rich substrate habitats within
warmer waters much farther north, near the
modern Peru-Ecuador border and beyond. Fish
species identified at Almejas also argue for the
presence of a local warm-water estuarine envi-
ronment with one or more inlets that afforded
access to the cooler offshore waters.

Subsistence

Although marine mollusks and fish were the
main food source, there is some evidence of
plant food use. Fragments of gourd rind (La-
genaria sicerarid) were found in the middle
levels of the cut, well below any evidence of
disturbance or contamination. Immature fruits
of this plant may have been used as food, and
the presence of rind fragments points to the use
of gourd containers. Other than gourd, only re-
mains of wild plants were recovered from the
preceramic midden. The dominant species was
algarrobo (Prosopis chilensis). Seeds of this
plant were very common, suggesting that the

sweet bean pods, readily available from trees
on the valley edges, were a source of food.

Warm-blooded vertebrates, including birds
and marine and terrestrial mammals, composed
an additional, relatively minor food source.
Bones of rails (Rallidae), cormorants (Phala-
crocorax spp.), mice (Cricetinae), sea lion
(Otariidai), and deer were identified among the
faunal remains within the stratigraphic excava-
tion (Reitz 1995b). However, none except the
mouse species is represented by more than one
or two bones.

The molluscan species inventory of Almejas
is unusual because it is dominated by shellfish
species, which favor the muddy, silt-rich sub-
strate typical of estuaries and are now available
almost exclusively in the warm-tropical waters
of the far north coast of Peru (Figs. 6 through
10). These include Chione subrugosa (Figs. 6
through 8), the most common species at Al-
mejas, as well as substantial numbers of Mytella
guyanensis (Figs. 6, 7, and 9), Mytella arcifor-
mis (Figs. 6, 7, and 10), Protothaca asperrima,
and Trachycardium procerum, and, more rarely,

Paleoenvironment at Almejas

Percentage of Shellfish Species by Weight

Leve,

1b
2a
2b
3a
3b
4a
4b
4c
4d
4e
5

Y7777\
V77A

VTA

Y/////////X
Y777A

Y/////////7777)(
Y/////////7777A
Y/////////7777\
V////////////A

V////////A

V//////X

V///////X

V///////A

I I

I Q I I
B I B

I I

i i o e

I I B B

I I Q B

I I fl

Figure 7. Diagram of shellfish species frequency through time at Almejas based on weight of sample. Level 5
is the earliest level; level la is the latest.

Mactra fonsecana, Nassarius luteostoma, Cer-
ithium stercusmuscarum, and Cerithidea albon-
odosa (Figs. 6 and 7) (Keen 1 97 1:63-6 10 pas-
sim; Olsson 1961:113-325 passim). Even
slightly later local preceramic and early ceramic
middens contain few to none of these species,
which suggests that they disappeared from the
area quite early. Not all shellfish from Almejas
are species that inhabit exclusively a mud flat
habitat. Tagelus dombeii (Figs. 6 and 7) is
known to occur in sandy substrates (Coker, cit-
ed in Dahl 1909:160), and this species has a
known range that extends northward to Panama
and southward to Chile (Dall 1909:160; Keen
1971:246; Olsson 1961:351). Also significantly,
shellfish typical of warm-temperate waters are
represented by a number of chiton plates and
shells of Tegula atra, Brachidontes purpuratus,
Thais chocolata, Choromytilus chorus, and lim-
pets (Figs. 6 and 7). These species characteristic
of colder water were accessible in the rocky
areas washed by open surf near the modern
town of Puerto Casma. They were much more
frequently exploited later, and came to domi-

nate the faunal inventory of sites established in
the area after the silting in and eventual desic-
cation of the estuary near Almejas. Clearly, the
inhabitants of Almejas placed much greater em-
phasis on the abundant and more readily acces-
sible shellfish within the local estuary, a rich
microenvironment teeming with plant and ani-
mal life.

The medium to large bivalve shells from Al-
mejas exhibit consistent fracture patterns (Figs.
8 to 1 0), which indicates they were bashed open
with a simple pounding tool. Because cooked
shellfish are easily opened, it seems most likely
that the inhabitants of Almejas consumed local
mollusks raw.

Fish species consumed by the inhabitants of
Almejas also reflect the site's proximity to the
resource-rich local estuarine environment. Bar-
rier islands protect such environments from the
ocean, promoting the deposition of the fine riv-
er-borne sediments that compose the component
mud flats and facilitate the formation of marsh-
es (Odum 1971:352-362). Nevertheless, estu-
aries experience tidal fluctuations through open-

5. Pozorski and T. Pozorski

Figure. 8. Whole and fragmentary specimens of Chione subrugosa showing the characteristic breakage pattern
evincing live shellfish consumption.

MET( ? 1C 'I , 21 , 31 , 4, , 5, . 61 . 71 8

Figure 9. Fragmentary specimens of Mytella guyanensis showing the characteristic breakage pattern evincing
live shellfish consumption.

Paleoenvironment at Almejas

Figure 10. Whole and fragmentary specimens of Mytella arciformis showing the characteristic breakage pattern
evincing live shellfish consumption.

ings that connect the estuary with a nearby bay
or open ocean (Odum 1971; Reitz 1995b). The
resulting environment is dynamic and much
more productive than offshore waters because
nutrients tend to be trapped and concentrated
there, and photosynthesis occurs throughout the
year (Odum 1971). Especially relevant to the
Casma situation is the fact that estuaries func-
tion as nurseries for many organisms, including
fish, thereby increasing their natural richness
(Odum 1971:356). Adult fish may spawn in the
ocean, with the larvae being carried into the
estuary by tidal currents. Other adult fish may
enter the estuaries to spawn, with their young
remaining there until they reach maturity. Adult
fish may spend more or less time within estu-
aries. They are attracted by the rich biomass as
a food source, yet temporarily intolerable tem-
peratures or salinity may induce them to leave
the estuarine ecosystem for more stable off-
shore water (Reitz 1995b; Hackner et al. 1976,
cited in Reitz 1995b). Other species that fre-
quent shallow near-shore waters may be attract-
ed to the vicinity of estuary inlets and even into
the estuary because of the richer food supply
available in such zones.

Since the estuary near Almejas was such a
critical part of the ecosystem which supported
the site's inhabitants, it is important to assess
the fish species relative to their potential role
within this feature of the local environment. To
accomplish this, we used Reitz's (1995b) ex-
cellent review and synthesis of the available
habitat data for the fish species identified from
Almejas, which draws primarily on Chirichigno
(1974, 1982) and Schweigger ( 1 964) as well as
additional sources (DEIS 1978; Hoese and
Moore 1977; Moreno and Castilla n.d. all cit-
ed in Reitz 1995b). The results are presented in
Tables 2 through 4. These tables reveal that fish
species consumed at Almejas fall into three
principal groups: species that frequent estuaries,
species native to the warm-temperate waters of
the Peruvian Current, and mixed-habitat species
that are known to inhabit both warm-temperate
and warm-tropical waters. Significantly, only
three species that are more typical of warm-
tropical waters were identified among the fauna!
remains. Several estuarine species were initially
classified as warm-tropical species (Reitz
1995b); however, assessment of fish habitat
data in light of the reconstructed local estuarine

S. Pozorski and T. Pozorski

TABLE 2. Fish species identified from the column sample.

MNI

Biomass*

Weight,

Species

NISP

No.

(%)

Estuarine fish species

Elops affinis (ladyfish)

(1.54)

0.039

0.0122

(1-79)

Clupeidae (herrings)

806

(29.23)

6.639

0.1713

(25.18)

Engraulidae (anchovies)

4,809

(51.54)

8.840

0.2142

(31.49)

Ariidae (sea catfishes)

(2.31)

0.140

0.0032

(0.47)

Bairdiella spp. (silver perch)

(0.77)

0.030

0.0029

(0.43)

Mugil spp. (mullet, lisa)

105

(6.92)

1.128

0.0322

(4.73)

Subtotal

120

(92.31)

0.4360

(64.09)

Warm-temperate fish species

Myliobatidae (eagle rays)

(1.54)

0.110

0.0198

(2.91)

Sciaena spp. (lorna)

(2.31)

0.028

0.0037

(0.54)

Subtotal

(3.85)

0.0235

(3.45)

Mixed-habitat fish species

Elasmobranchiomorphi

(cartilaginous fishes)

(0.77)

0.009

0.0022

(0.32)

Dasyatidae (stingrays)

(0.77)

0.070

0.0128

(1.88)

Muraenidae (morays)

(0.77)

0.010

0.0008

(0.12)

Cynoscion spp. (seatrout)

(0.77)

0.020

0.0022

(0.32)

Subtotal

(3.08)

0.0180

(2.64)

Warm-tropical fish species

Gerridae (Mojarras)

(0.77)

0.009

0.0006

(0.09)

Subtotal

(0.77)

0.0006

(0.09)

Unidentified fish

849

8.340

0.2022

(29.72)

Abbreviations: NISP, number of identified species; MNI, minimum number of individuals.

* Biomass values are based on calculations made by Reitz (1995b; Reitz and Cordier 1983; Reitz et al. 1987).

environment led the authors to conclude that
virtually all of these species should more ap-
propriately be viewed as estuary dwellers. The
differences between the fish species identified
from the column sample as compared to the
general excavation (Tables 2 and 3) are partic-
ularly noteworthy in this regard. The fish re-
mains from the column sample (no. 10 and no.
25 geological sieves) strongly reflect exploita-
tion of the estuary, where small fishes, both
young fishes and small adult fishes, could be
easily taken. The small herrings and anchovies
are included in Table 2 as estuarine fish because
some species within both families are known to
frequent estuaries and because their consistent,
small size within the archaeological sample
suggests that the estuary served as their nurs-
ery. In contrast, adults of these two species are
known to frequent the offshore waters of the
Peruvian Current; therefore, the herring and an-

chovy remains recovered from the general ex-
cavation (V4 in. screen) were included among
the warm-temperate fish in Table 3. Tables 2
and 3 also reveal the paramount importance of
the estuary as a food source. More than 64% of
the fish biomass reconstructed for the column
sample came from estuarine fishes, versus
3.45% for the warm-temperate fishes and
2.64% for the mixed-habitat fishes (Table 2).
More balance can be seen with respect to the
fish biomass reconstructed for the general ex-
cavation, with almost 24% comprised of estu-
arine species, over 21% comprised of warm-
temperate species, and over 14% comprised of
mixed-habitat fish (Table 3). These proportions
are in keeping with the reconstructed subsis-
tence scenario. Adult mullet and sea catfish are
known to inhabit estuaries and have been clas-
sified accordingly. The other adult species rep-
resented by vertebrate remains from the general

Paleoenvironment at Almejas

TABLE 3. Fish species identified from the general excavation.

MNI

Biomass*

Weight,

Species

NISP

No.

(%)

Estuarine fish species

Albula vulpes (bonefish)

(0.97)

0.080

0.0041

(0.10)

Ariidae (sea catfishes)

220

(20.39)

39.170

0.6858

(17.26)

Micropogonias spp. (croaker)

(4.85)

2.760

0.0949

(2.39)

Mugil spp. (mullet, lisa)

114

(14.56)

8.000

0.1665

(4.19)

Subtotal

(40.77)

50.010

0.5913

(23.94)

Warm-temperate fish species

Myliobatidae (eagle rays)

(0.97)

0.430

0.0609

(1.53)

Clupeidae (herrings)

150

(10.68)

4.669

0.1089

(2.74)

Engraulidae (anchovies)

(3.88)

0.168

0.0081

(0.20)

Pamlabrax spp. (cabrilla)

(3.88)

0.560

0.0094

(0.24)

Trachurus murphvi

(jack mackerel, jurel)

(3.88)

2.350

0.0885

(2.23)

Anisotremus spp. (sargo)

(0.97)

0.080

0.0030

(0.08)

Sciaenidae (drums)

0.760

0.0318

(0.80)

Paralonchurus spp. (coco)

(4.85)

9.080

0.2642

(6.65)

Sciaena spp. (lorna)

(7.77)

1 1 .260

0.2421

(6.09)

Bodianus spp. (hogfish)

(0.97)

0.270

0.0093

(0.23)

Sarda spp. (bonito)

(0.97)

0.790

0.0226

(0.57)

Subtotal

(38.83)

30.417

0.8488

(21.36)

Mixed habitat fish species

Carcharhinidae (requiem sharks)

(2.91)

1.360

0.1864

(4.69)

Dasyatidae (stingrays)

(2.91)

1.720

0.2249

(5.66)

Muraenidae (morays)

(0.97)

0.030

0.0019

(0.05)

Serranidae (sea basses)

0.200

0.0033

(0.08)

Carangidae (jacks)

0.130

0.0065

(0.16)

Trachinotus spp. (pompano)

(0.97)

0.050

0.0028

(0.07)

Cynoscion spp. (seatrout)

(5.83)

1.620

0.0759

(1.91)

Bothidae (flounders)

(2.91)

2.520

0.0639

(1.61)

Subtotal

(16.50)

7.630

0.5656

(14.24)

Warm-tropical fish species

Epinephelus spp. (grouper)

(2.91)

2.630

0.0522

(1.31)

Gerridae (Mojarras)

(0.97)

0.210

0.0075

(0.19)

Subtotal

(3.88)

2.840

0.0597

(1.50)

Unidentified fish

1,810

1 1 1 .900

1.5473

38.95

Abbreviations: NISP, number of identified species; MNI, minimum number of individuals.

* Biomass values are based on calculations made by Reitz (1995; Reitz and Cordier 1983; Reitz et al. 1987).

excavation are potential offshore species that
may have been taken in the cooler waters of the
open ocean, near estuary inlets because of the
richer nutrients, or even within the estuary
the richest of the three potential environments.
This is especially likely for sargo (Anisotremus
spp.), seatrout (Cynoscion spp.), coco (Paralon-
churus spp.), lorna (Sciaena spp.), flounders
(Bothidae family), and members of the jack
family (Carangidae), all of which are known to
inhabit shallow inshore waters.

Environment

The archaeological data from Almejas must be
viewed in relation to three radiocarbon dates
from its midden: 5245 75 B.C. (UGa-4518),
5270 70 B.C. (UGa-4519), and 4925 105
B.C. (UGa-4539) (Table 1 ). These dates cluster
around 5000 B.C. (uncalibrated). Several other
sites along the western coast of South America
are known to date as early as Almejas or earlier.
The earliest coastal sites that show heavy reli-

S. Pozorski and T. Pozorski

TABLE 4. Combined biomass values for fish species identified at Almejas.*

Estuarine fish
species

Warm-temperate
fish species

Mixed-habitat
fish species

Warm-tropical
fish species

Unidentified
fishes

Sample

General excavation

0.9513

(23.94)

0.8488

(21.36)

0.5656

(14.24)

0.0597

(1.50)

1.5473

(38.95)

Column

sample

0.4360

(64.09)

0.0235

(3.45)

0.0180

(2.64)

0.0006

(0.09)

0.2022

(29.72)

Adjusted

columnt

5.7988

(64.09)

0.3125

(3.45)

0.2394

(2.64)

0.0080

(0.09)

2.6893

(29.72)

Total

6.7501 (51.84) 1.1613 (8.92) 0.8050 (6.18) 0.0677 (0.52) 4.2366 (32.54)

* Biomass values are based on calculations made by Reitz (1995b; Reitz and Cordier 1983; Reitz et al. 1987).
t The column sample values were adjusted upward based on the proportion that the column sample volume (109
liters) represented of the total volume of the stratigraphic excavation (1,454 liters), resulting in a factor of 13.3.

ance on marine resources are known from the
far north of Peru near Talara (Richardson 1978,
1981), in southern Ecuador (Stothert 1985),
from far southern Peru near Ilo (Sandweiss et
al. 1989), and from northern Chile near Anto-
fagasta (Aldenderfer 1989:117-144; Llagostera
Martinez 1979; Richardson 1981, 1994:38-39).
These sites tend to be located where the conti-
nental shelf is narrow, thereby minimizing the
impact of the subsequent shoreline transgres-
sion believed to have inundated ancient shore-
line sites where the shelf is wide (Richardson
1981). These sites also tend to have faunal re-
mains consistent with their geographic location.

Three additional sites or site complexes are
more comparable to Almejas based on their ra-
diocarbon dates and because of the presence of
what have been described as thermally anoma-
lous fish and/or shellfish species. These include
the Paijan complex sites, located well inland
between the Chicama and Jequetepeque Val-
leys, which have been dated to approximately
8550-6050 B.C. (Chauchat 1988; Reitz 1995a,
1995b), as well as Ostra Base Camp and Pampa
las Salinas, located north of the Santa River
mouth, with radiocarbon dates of ca. 6000 B.C.
(Reitz 1995a, 1995b, 2001; Sandweiss et al.
1983, 1986, 1996).

The data from Almejas are especially rele-
vant to the controversial issues of when the sea
level attained its present level and the antiquity
of the present climatic regime and its associated
current patterns (DeVries and Wells 1990;
DeVries et al. 1997; Kerr 1999; Rodbell et al.
1999; Rollins et al. 1986, 1997; Sandweiss
1986; Sandweiss et al. 1983, 1996, 1997, 1998,
1999; Wells 1988:160-176; Wells and Noller
1997). The authors' reconstruction of the en-
vironment of Almejas at the time of its occu-

pation suggests that the sea level and climatic
conditions in effect today are in fact quite old.

The warm-temperate water of the Peruvian
Current was likely present off the Casma Valley
coast at least by about 7000 years ago, when
Almejas was occupied. Arguments for consid-
erable antiquity for the current climatic regime
are based on the faunal inventory of Almejas,
subsistence activities practiced at the site, and
preservation within the site. Both fish and shell-
fish species provide evidence that cold water
was readily accessible from the site. Additional
evidence that these species characteristic of
warm-temperate water were taken by the inhab-
itants of Almejas comes from the human skel-
eton, which was characterized by auditory ex-
ostoses, bony growths that develop in the ear
canal as a result of repeated exposure to cold
water (Kennedy 1986). Finally, the preservation
of fragile plant material including the junco
burial wrapping, gourd rind, and algarrobo
seeds within the Almejas midden argues for a
near-rainless climate of the type that exists to-
day. Without the Peruvian Current offshore, the
climate would have been significantly wetter,
and preservation would have been negatively
affected.

Sea level was probably close to or slightly
higher than current levels at the time Almejas
was in use (Wells 1988:161-162). Evidence for
this comes from the fact that an estuary was
present at the mouth of the Casma River at this
time (Wells 1988:161-162). Formation of this
estuary depended on the sea level being at or
slightly above its present height. Ample evi-
dence for the existence and exploitation of this
rich estuarine environment comes from the
many warm-water mud flat molluscan species
and the estuarine fish species, especially the im-

Paleoenvlronment at Almejas

mature individuals recovered through fine
screening, that make the Almejas faunal inven-
tory so remarkable. These species most likely
became established in the estuarine environ-
ment when free-floating or free-swimming mol-
luscan larvae and fish traveled south within the
warm Ecuadorian Countercurrent during an in-
frequent El Nino event. They would have
thrived within the shallow, nutrient-rich, sun-
warmed estuarine environment (DeVries and
Wells 1990; Smith 1944:v). The Casma Valley
is an especially favorable place for this to occur
because of the large number of sunny days
(ONERN 1972:50).

Warm-temperate species were available on
the rocky headlands and slightly offshore, but
mud flat estuarine species were clearly pre-
ferred. This preference probably reflects both
their abundance in the rich estuarine habitat and
their ease of capture, especially for people who
apparently lacked a well-developed fishing
technology. Nutrients from the estuarine envi-
ronment would have spilled out into the ocean,
thereby attracting warm-temperate fish and
making them more accessible to the people of
Almejas.

Ironically, the same sea level rise or trans-
gression that initially facilitated development of
the estuarine environment that likely attracted
the inhabitants of Almejas to settle nearby also
triggered deposition of river-borne sediments
(DeVries and Wells 1990; Wells 1988:172-
176). Gradual filling by these sediments ulti-
mately eliminated the estuary a local environ-
mental change that also likely led to the aban-
donment of Almejas. Similar sequences of es-
tuary development and backfilling by
river-borne sediment likely occurred in other
coastal areas, thereby also explaining occasion-
al occurrences of colonies of tropical fauna of
relatively long duration within an otherwise
temperate zone. This would also explain why
estuaries were once more common, but are now
rare.

Variation in the frequency of specific shell-
fish species through time may be correlated
with the gradual silting in of the estuarine en-
vironment that eventually led to its disappear-
ance and the abandonment of Almejas. The
charts in Figures 6 and 7 clearly reveal that six
species comprise most of the molluscan inven-
tory: Mytella arciformis, Protothaca asperima,
Mytella guayanensis, Chione subrugosa, Tage-
lus dombeii, and Trachycardium procerum,

with the latter showing a significant presence
more clearly in Figure 7. It is also readily ap-
parent that Mytella arciformis dominates the
shellfish inventory in the earliest levels and that
Protothaca asperima and Mytella guayanensis
exhibit their greatest frequencies of occurrence
slightly later within the stratigraphic sequence.
Tagelus dombeii peaks in frequency even later
in the sequence, whereas Chione subrugosa, the
most abundant mollusk overall, exhibits its
highest frequency toward the end of the strati-
graphic sequence.

Habitat data are rarely supplied in great de-
tail, but the data available for the principal spe-
cies indicate that two of the three species that
predominate in the early and early-middle por-
tion of the sequence are known to occur in con-
siderably deeper water than most species that
predominate in the late and middle-late portion
of the sequence. Specifically, the habitat of My-
tella arciformis has been described as "six fath-
oms, mud" (Hertlein and Strong 1946:72), and
Prothaca asperrima has been described as oc-
curring "in sandy mud at a depth of 13 fath-
oms" (Hertlein and Strong 1946:187). When
specific depth measurements are provided for
one species with peak frequencies toward the
latter part of the sequence, the habitat depth is
much shallower. Live specimens of Tagelus
dombeii are described as being "taken in sand
under three or four feet of water" (Coker, quot-
ed in Dahl 1909:160). However, live individuals
of Trachycardium procerum, which are slightly
more abundant during the latter portion of the
sequence, were "found in coarse sand in from
four to six fathoms of water" (Sowerby 1833:
83), and each of the six dominant species has
been described by one or more experts as oc-
curring in shallow water, lagoons, shallow la-
goons, on mud flats, at low water, and in inter-
tidal zones, indicating that all could be found
at times in relatively shallow water (Hertlein
and Strong 1946:72-191 passim; Keen 1971:
63-246 passim; Olsson 1961:298; Soot-Ryen
1955:53, 55; Sowerby 1835:41).

When the available data on the geographic
distribution of the principal species are consid-
ered, the three species with peak frequencies
earlier in the sequence appear more narrowly
confined to warm-tropical zones. Mytella arci-
formis is known from El Salvador to Ecuador
or Peru (Hertlein and Strong 1946:72; Keen
1971:63), Mytella guayanensis is known from
Mexico or the Gulf of California to northern

S. Pozorski and T. Pozorski

Peru (Hertlein and Strong 1946:72-73; Keen
1971:63; Soot-Ryen 1955:53, 55), and Proto-
thaca asperrima is known from California to
Peru more commonly northern Peru (Dahl
1909:158; Hertlein and Strong 1946:187; Keen
1971:193). In contrast, Tagelus dombeii is
known from Panama to Chile (Dahl 1909:160;
Keen 1971:246; Olsson 1961:351); Chione sub-
rugosa is described by Dahl (1909:158) as oc-
curring from the Gulf of California to Valpa-
raiso, Chile (although other experts describe a
more northern range, from the Gulf of Califor-
nia to Peru: Hertlein and Strong 1946; Keen
1971:190; Olsson 1961:298); and Trachycar-
dium procerum is known from the Gulf of Cal-
ifornia to northern Chile or Chile (Keen 1971:
155; Olsson 1961:247-248). These data likely
reflect the greater tolerance of Chione subru-
gosa, and especially Tagelus dombeii and Tra-
chycardium procerum, to more varied environ-
ments, including cooler water. This may have
allowed these species to survive as the estuary
filled with silt, became smaller in area, and was
likely more impacted by the cooler water of the
adjacent open ocean at its outlet. Such an in-
terpretation might also explain the relatively
rare but continued presence of remains of these
three species at later preceramic and Initial Pe-
riod (1800-900 B.C.) sites.

Discussion and Conclusions

As a result of recent fieldwork and research,
other archaeological sites similar to Almejas
have been discovered that date quite early with-
in the Andean sequence and have yielded faunal
assemblages that reflect the presence of species
not currently typical of their respective lati-
tudes. These include the Paijan complex sites
north of the Chicama Valley and the sites of
Pampa las Salinas and Ostra Base Camp north
of the Santa River mouth (Andrus et al. 2002;
Chauchat 1976, 1978, 1988; Reitz 1995a,
1995b, 2001; Rollins et al. 1986; Sandweiss et
al. 1983, 1996).

Initially, the sites north of Santa attracted at-
tention because of the presence of shellfish cur-
rently known to inhabit warm-tropical waters
(Rollins et al. 1986; Sandweiss et al. 1983), as
did the site of Almejas. These data from the
Santa sites in particular were initially used to
argue for the continuous presence of warmer

currents much further south, an absence of
ENSO events, and a corresponding wetter cli-
matic regime much different from today's cli-
mate (Rollins et al. 1986; Sandweiss et al.
1983). As additional faunal material was ana-
lyzed from the Paijan complex sites, from the
Santa area, and from Almejas in Casma, fish
species were identified that are not currently
typical of these areas. These results have been
used by many of the same investigators as fur-
ther evidence of the presence of warmer off-
shore waters (Andrus et al. 2002; Reitz 1995a,
1995b, 2001; Sandweiss et al. 1996).

An alternative scenario maintains that the
current climatic regime, including periodic
ENSO events, is quite ancient. Indeed, evidence
from the far south coast site of Quebrada Ta-
cahuay indicates that ENSO events were pre-
sent at least as early as the late Pleistocene
(Keefer et al. 1998). The seemingly out-of-
place species represent colonies of thermally
anomalous fauna whose larvae were carried
southward within the warm currents of a peri-
odic ENSO event (S. Pozorski and T. Pozorski
1995; DeVries et al. 1997; Wells and Noller
1997). As the sea level rose to approximately
modern limits, estuaries formed at the mouths
of some rivers, and the resultant shallow, sun-
warmed, nutrient-rich waters readily supported
species adapted to warmer estuarine waters
(DeVries et al. 1997; DeVries and Wells 1990;
Wells and Noller 1997). Also according to this
scenario, ENSO events were essential to stock
the estuaries with appropriate fish and shellfish
species, after which time the cooler offshore
Peruvian Current would have returned. Once in-
troduced, these warm-tropical shellfish and fish
species would have flourished in these estuaries
as long as local environmental conditions re-
mained favorable. Subsequent ENSO events
could potentially have introduced additional
shellfish and fish species, but such events were
not essential for the survival of these species in
their localized estuarine environments. Hence,
fluctuations in the periodicity of ENSO events
are not especially relevant with respect to the
survival of these thermally anomalous shellfish-
es and fishes in estuarine conditions. The criti-
cal variable was the maintenance of local en-
vironmental conditions. Ironically, the same sea
level rise that precipitated the formation of es-
tuarine environments was also a causal factor
in their disappearance as river-borne sediments
infilled these coastal features. This explains the

Paleoenvironment at Almejas

near absence of estuaries along the modern Pe-
ruvian coast.

Clearly, faunal data from the Paijan complex
sites, the Santa sites, and Almejas are critical to
address the issue of past climate in the vicinity
of these sites. In assessing these fauna, partic-
ularly the fish species, the tendency has been to
emphasize, and at times "force" the data to
conform to, the perceived dichotomy between
(1) species that are characteristic of the warmer
water off the coast of Ecuador and northern
Peru and have been classified as warm-tropical
species and (2) species that are characteristic of
the cooler water of the Peruvian Current and
have been classified as warm-temperate species
(Reitz 1995a, 1995b, 2001; Sandweiss et al.
1996). To Reitz's credit, she discusses the prob-
able existence of estuaries in the respective vi-
cinities of Ostra Base Camp, Almejas, and Pai-
jan complex sites, states the important charac-
teristics of estuaries and their fauna, meticu-
lously reviews habitat data for the species
identified at the sites, and describes many of the
fish species identified at the sites as estuarine
fishes. Nevertheless, in the final analysis, she
categorizes these typically estuarine fishes as
warm-tropical species (Reitz 1995a, 1995b,
2001). In contrast to this approach, we believe
that the marine fauna of the three sites under
consideration here should be examined in light
of the prevalent environments at the sites: es-
tuaries and offshore warm-temperate waters.

Tables used by Sandweiss et al. (1996:Table
3; Reitz 1995a:Table 1, 1995b:Table 2) to show
broad trends on the basis of MNI (minimum
number of individuals) percentages for what
they classified as warm-tropical versus warm-
temperate fish species resulted in high values
for warm-tropical species from Paijan sites, Os-
tra Base Camp in the Santa area, and Almejas.
Although nonmarine vertebrates figured more
prominently in the subsistence regimen of the
Paijan sites, the identifiable fish (MNI =113)
were assessed at 97.3% warm-tropical species
versus 2.6% warm-temperate species. For the
Ostra Base Camp site, the values were 64.2%
warm-tropical species and 35.8% warm-tem-
perate species (MNI = 120). For Almejas, the
values also included mixed-habitat species (spe-
cies known to occur in both warm-tropical and
warm-temperate waters), and the column sam-
ple and general sample were treated separately
(Reitz 1995a, 1995b). The Almejas results, as
tabulated by Reitz (1995a, 1995b), were as fol-

lows: 40% warm-tropical, 35% warm-temper-
ate, and 15% mixed for the general excavation
(MNI ---- 114), and 12% warm-tropical, 84%
warm-temperate, and 4% mixed for the column
sample (MNI = 131).

These data presented by Reitz (1995a, 1995b,
2001) and Sandweiss et al. (1996) would seem
to indicate the presence of warm offshore wa-
ters in the vicinities of the three sites. However,
closer examination of the individual fish species
and their habitats suggests to the authors that
most fishes classified as warm-tropical species
are more appropriately classified as estuarine
species. This has already been demonstrated for
Almejas (described above), for which detailed
data are available to the authors. Once estuarine
species have been reclassified, few species
identified at Almejas remain within the warm-
tropical category (Tables 2 to 4). Detailed spe-
cies lists for Paijan complex sites have not been
published; however, Reitz (1995b, 2001) de-
scribes sea catfish (Ariidae) and lisa (mullet,
Mugil spp.) as the most common fishes, with
bonefish (Albula vulpes) and croaker (Micro-
pogonias spp.) common in some assemblages
and small numbers of mojarra (Gerridae, Eu-
cinostomus spp.) and porgy (Sparidae) also
identified. Herring (Clupeidae), anchovy (En-
graulidae), and coco (Paralonchurus spp.) were
also present. Among these species listed for the
Paijan complex sites, all are commonly found
in estuaries except adult herring, anchovy, and
coco (Paralonchurus spp.), which are warm-
temperate species, and mojarra (Gerridae), the
only fish listed that is typically taken in warm-
tropical waters (Reitz 1995b). Fewer data are
available concerning fish species identified at
Ostra Base Camp; however, Reitz (1995a,
2001) mentions bonefish, sea catfish, lisa (mul-
let), and puffer (Spheroides annulatus) as the
primary species, with warm-temperate fishes
relatively rare. All of these primary species
mentioned for Ostra Base Camp are estuarine
fishes (Reitz 1995b, 2001).

Data from the fine-screened column sample
we excavated at Almejas were also critical to
our realization that subsistence activities at this
site were focused primarily on the local estua-
rine ecosystem and its component resources.
These tiny bones represent small fishes and es-
pecially the young of species that typically use
estuaries as nurseries. Their importance to the
inhabitants of Almejas is especially evident
when their respective biomass values are ad-

S. Pozorski and T. Pozorski

justed to compensate for the difference in vol-
ume between the column sample and the gen-
eral excavation (Table 4). Mud flat mollusks,
also typical of estuaries, composed the other
major source of food for the people of Almejas.
These shellfishes provide additional evidence of
the importance of this resource zone to their
subsistence. The location of the site and the in-
habitants' decision to settle near the mouth of
the Casma River were likely predicated on the
rich and abundant estuarine resources, and the
site was likely abandoned once the estuary silt-
ed in and disappeared. Nevertheless, the pres-
ence of substantial amounts of warm-temperate
fish species along with a number of molluscan
species known to inhabit warm-temperate wa-
ters provides evidence that warm-temperate
species were accessible to and exploited by the
site's occupants. These species also document
the presence of the cooler offshore waters of
the Peruvian Current in the vicinity of the site.
The data presented and reviewed here reveal
that the site of Almejas is unusual for several
reasons. It represents one of the earliest marine-
oriented sites along the north and central coast
of Peru, predating by at least 2000 years most
of the larger, better known sites dating to the
Late Preceramic Period. Its shellfish and fish
inventories also distinguish Almejas from most
known preceramic sites and provide critical ev-
idence that subsistence activities by the site's
inhabitants focused on a local estuarine envi-
ronment complemented by some exploitation of
warm-temperate offshore waters. Coincident
geomorphological data indicate that modern sea
level had been attained by the time Almejas
was occupied, resulting in the formation of the
estuarine environment that attracted these early
settlers. Finally, the faunal remains, the geo-
morphological data, and archaeological evi-
dence of optimum preservation argue that the
ENSO phenomenon has been in existence since
at least 5000 B.C., and probably much longer.

Acknowledgments. Permission to excavate at
Almejas was granted by the Institute Nacional
de Cultura, and funding for the excavation was
provided by grants from the O'Neil and Netting
Funds of the Carnegie Museum of Natural His-
tory. Funds for the radiocarbon assays were
provided by grant BNS-8203452 from the Na-
tional Science Foundation. Vertebrate faunal re-
mains from Almejas were identified by Eliza-
beth Reitz of the Museum of Natural History,

University of Georgia, with funding from the
Faculty Research Council at the University of
Texas-Pan American. Interpretations of the re-
sults of this faunal analysis within this paper,
including tables constructed by the authors us-
ing Reitz's identifications and biomass recon-
structions, reflect the opinion of the authors.

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The Impact of the El Nino Phenomenon on

Prehistoric Chimu Irrigation Systems

of the Peruvian Coast

Thomas Pozorski and Shelia Pozorski

Long-abandoned prehistoric irrigation systems
are a common feature of the landscape in many
Peruvian coastal valleys. Some of the most im-
pressive examples of prehistoric irrigation sys-
tems can be found between the La Leche Valley
and the Viru Valley on the north coast of Peru
(Kosok 1965). These remains of canals and oc-
casional fields, which currently lie outside the
limits of modern irrigation, are believed to date
to about B.C./A.D. or later, within Early Inter-
mediate Period (200 B.C.-A.D. 600) through
Late Intermediate Period (A.D. 1000-1470)
times. Studies of these exceptionally well-pre-
served remains of ancient land reclamation fea-
tures reveal that their planners and builders
faced a variety of challenges, including diffi-
culties presented by local topography, the na-
ture of the substrate, and periodic climatic var-
iation, especially the notable impact created by
strong El Nino rains that hit the Peruvian north
coast a few times each century. Some challeng-
es were effectively met through varied and of-
ten ingenious engineering feats. Other challeng-
es were never successfully overcome despite
the expenditure of vast amounts of labor. To
ameliorate the effects of such engineering fias-
cos, alternative strategies were developed to
compensate for production lost as a result of
failed reclamation efforts.

The data and conclusions presented here are
the result of fieldwork within the Moche and
Chicama Valleys during the late 1970s by the

Programa Riego Antiguo archaeological pro-
ject. This project involved intensive survey
and mapping of the prehistoric irrigation sys-
tems outside the limits of modern cultivation
within the Moche Valley, as well as study of
the area between the Moche and Chicama Val-
leys traversed by the Chicama Moche Inter-
valley Canal. All of these areas with preserved
prehistoric canals were explored further
through excavations that transected the canal
channels and by means of occasional horizon-
tal clearing. The Moche and Chicama prehis-
toric irrigation systems had been subject to
surface survey and limited test excavations
prior to the Programa Riego Antiguo archae-
ological project (Farrington 1974, 1980; Far-
rington and Park 1978; Kosok 1965; Kus
1972). It was evident from the beginning of
the project, however, that intensive excavation
would be needed to sort out the complex na-
ture of these systems and their relationships
with the prehistoric sites in the area; the so-
cieties that built, maintained, repaired, and ul-
timately abandoned them; and the surrounding
environment that was subjected to periodic El
Nino rains. Through detailed study of the sur-
face evidence and excavated canal profiles and
features, it was possible to develop a detailed
chronology of the growth and decline of the
irrigations systems, including when and how
they were affected by El Nino rain.

T. Pozorski and S. Pozorski

Cerro
Campana /

Intervalley Canal

Pampa

Pampa
Rio Seco

, Cerro
s Cabras

PampaN

Esperanza\ Vichansao
Canal

Caballo
Muerto

Chan

Moche River,

Cerro I
Blanco

Modern Cultivation

Hill

Bluff

Figure 1. Map of the Moche Valley showing the extent of modern cultivation, the Three-Pampa area, prehistoric
canals outside of modern cultivation, and relevant archaeological sites.

The Archaeological Evidence

Canals and Fields

The extremely arid climate of coastal Peru fos-
ters excellent preservation of archaeological re-
mains, including the prehistoric agricultural
features that extend beyond the limits of mod-
ern cultivation (Figs. 1 and 2). These range
from major and minor canals to fields with in-
tact furrows (Fig. 3). Within the Moche Valley,
several small prehistoric canal systems are pre-
served on both sides of the river; however, the
greatest expanse of preserved canals and fields
lies well down-valley, toward the ocean. This
latter zone, which contains Pampas Esperanza,
Rio Seco, and Huanchaco, has been designated
the Three-Pampa area (Figs. 1 and 2). In late
prehistoric times, an effort was made to draw
water into the Three-Pampa portion of the sys-
tem from the Chicama River in the next valley
north via the unsuccessful Chicama-Moche In-
tervalley Canal. This tremendous undertaking is

well documented in the archaeological remains
(Kosok 1965:90-94; T. Pozorski 1987; T. Po-
zorski and S. Pozorski 1982).

Within the Moche Valley, the largest canals
in the archaeological record actually represent
now-abandoned extensions of canals still in use
along much of their lengths. These canals were
designed for water transport; they drew water
directly from the Moche River. A hierarchical
system of increasingly smaller canals carried
water from each major canal to associated sets
of fields.

Excavations that transected canals and fields
revealed the history of their construction and
use or lack of use. As expected, major canals
contained a succession of numerous channels,
reflecting their permanence upon the landscape
and long-term use. Successively smaller canals,
and especially fields, contain correspondingly
fewer distinct channels, reflecting the fact that
smaller elements of the total system were more
ephemeral. When the profiles of transected ca-
nals were examined, individual channels could

Prehistoric Chimu Irrigation Systems

|/ /\ Modern cultivation

Figure 2. Map of the Three-Pampa area showing the major irrigation canals that lie north of Chan Chan.

be distinguished by the nature of their compo-
nent sediments; and these channels or major
use episodes could be traced from profile to
profile along the length of major canals and
many minor canals. Based on these connections
among canal channels, it was possible to de-
velop a sequence for the construction and use
of the portion of the prehistoric Moche Valley
canal system outside modern cultivation.

Evidence of Canal Use

Profiles of transected canals also yielded infor-
mation on the duration and intensity of canal
use. Canal use was reflected archaeological ly
mainly in two ways. First, within the active
channel, laminar sediments were formed as wa-
ter-borne material left in suspension or surface
deposits blew in and were arranged in a laminar
configuration by the water flow (Fig. 4). Fre-
quently, this deposition constituted the process
by which the initially excavated channel stabi-

lized in response to water flow. Subsequent
changes in water velocity or quantity resulted
in erosion and/or deposition.

A second indicator of canal use was the dark
coloration of sediments or soils beneath a chan-
nel that resulted from water logging. When sed-
iments are subjected to repeated wet-dry epi-
sodes, oxidation occurs, turning the surfaces of
the individual soil particles first yellow to or-
ange and ultimately brown to dark red. Canals
observed in profile exhibited varying degrees of
oxidation from very slight to no discoloration
to intensive darkening 40 cm or more below the
active channel. When sediments are kept wet
for longer periods of time, waterlogging occurs,
turning soil particles gray to black in color.

Neither an evaluation of the deposition and
erosion of water-lain canal sediments nor a con-
sideration of the amount of associated oxidation
can be used to reconstruct absolute time spans
for canal use. However, when taken together,
they provide a relative indicator of the magni-
tude of use for a given channel. Based on the

T. Pozorski and S. Pozorski

^vT Si?m

,-.vW '.:. rft-^-Z

^-^t^* ^T

6s,:x;. r-'??^ r >g*t.-.

^^S|^:^

<^-r3B^

'? - t^^^^Bfcl* : - J^-l r ' "'- ' ;"' ^-. ^-.-x^

Figure 3. View of stone-lined Chimii canals along the east edge of Pampa Rio Seco.

same evidence, canals or channels lacking both
laminar sediments and oxidation never func-
tioned effectively. Such abortive canal seg-
ments often have additional characteristics that
precluded their effective use, such as an uphill
slope (T. Pozorski and S. Pozorski 1982).

Irrigation Systems
Prior to B.C./A.D.

Preserved remains of prehistoric irrigation sys-
tems date relatively late in the Andean se-
quence; however, there is general agreement
that irrigation agriculture had its beginning
much earlier. Most authors (Burger 1992:57;
Morris and von Hagen 1993:45; Moseley 1992:
126; Patterson 1985:67; S. Pozorski and T. Po-
zorski 1987:114; Richardson 1994:64; von Ha-
gen and Morris 1998:46) date the inception of
large-scale irrigation agriculture within Peruvi-
an valleys to the Initial Period (2150-1000
B.C.). (Dating is based on calibrated radiocarbon
dates using values supplied in Stuiver and

Becker [1993].) Experimentation likely oc-
curred even earlier, during the Late Preceramic
(3000-2150 B.C.), when most of the population
was concentrated in large settlements near the
coast. Small, short canals may have been con-
structed within or near the active flood plains,
which are a considerable distance from most
Late Preceramic sites. Such experimentation
with water control is suggested by the varied
inventory of cultivated species at Late Precer-
amic sites. These include squash, common
bean, potato, avocado, lima bean, lucuma, gua-
va, cansaboca, and especially gourd and cot-
ton industrial plants essential to the lives of
coastal fishermen (S. Pozorski 1987:16; S. Po-
zorski and T. Pozorski 1987:113, 1988:95-96;
T. Pozorski and S. Pozorski 1990:17-18).

Evidence for Initial Period irrigation is more
substantial. At this time large, complex sites
dominated by one or more platform mounds ap-
pear well inland in over 15 river valleys of the
north and central Peruvian coast. These mounds
are located at or near optimum zones for canal
intakes as if to effectively monitor or control
water use (Burger 1992:57; Morris and von Ha-

Prehistoric Chimu Irrigation Systems

Figure 4. View of laminar deposits within a now-abandoned prehistoric Chimu canal.

gen 1993:45; Moseley 1992:126; Patterson
1985:67; S. Pozorski and T. Pozorski 1987:114;
T. Pozorski 1982; Richardson 1994:64; von Ha-
gen and Morris 1998:40). In the Moche Valley
during the Initial Period, the irrigation system
probably extended down to the Caballo Muerto
Complex (Fig. 1). Many of the large mounds at
these sites also face up-valley or upriver, an ori-
entation that has been correlated with reverence
for the source of the river water so essential to
irrigation (S. Pozorski and T. Pozorski 1987:
114; Williams 1985:230). Subsistence data
available for this time period document a
marked increase in the variety and especially
the quantity of cultivated plants consumed and
used at Initial Period sites. Peanuts and manioc
are some of the food plants added to the pre-
historic diet at this time. Comparisons of sub-
sistence inventories for coastal and inland sites
suggest that marine resources continued to be
important and that satellites of the inland cen-
ters were established and maintained on the
coast to supply essential protein in exchange for
agricultural products (S. Pozorski and T. Pozor-
ski 1979, 1987:19-20).

Early Intermediate Period
Irrigation Systems Within the
Moche Valley

Within the Moche Valley, the earliest evidence
of prehistoric irrigation that expanded beyond
the limits of modern cultivation dates to the
Early Intermediate Period and is associated with
the Moche occupation of the valley. At this
time, the extent of cultivated land extended
slightly outside modern limits, encompassing
only Pampa Esperanza and a narrow strip with-
in Pampa Rio Seco along the west edge of Pam-
pa Esperanza (Figs. 5 and 6). With the excep-
tion of a single canal on Pampa Rio Seco that
lies near the modern surface, the Moche canals
are deeply buried, directly underlying subse-
quent Chimu use of the same channels.

The Moche and Chimu efforts to reclaim the
area are distinct, however, and can be distin-
guished on the basis of several lines of evi-
dence. Canal channels believed to have been
constructed during the Early Intermediate Pe-
riod are often directly associated with Moche
sites, and their extent corresponds to the extent

T. Pozorski and S. Pozorski

4 km

Blanco

[/ A Modern Cultivation
|r-^~| Hill

K\ v "| Bluff

Prehistoric Cultivation

Figure 5. Map of the Moche Valley showing the extent of prehistoric irrigation outside modern cultivation during
Moche times (A.D. 100-600).

of substantial Moche occupation of the Three-
Pampa area. Canal-bank sediments associated
with these deep channels contained occasional
Moche ceramics, but no later cultural material,
and one charcoal sample from a canal bank
yielded a radiocarbon date of A.D. 550 80 (T.
Pozorski 1987:Table 1). Finally, the natural
substrate beneath these canals is the most inten-
sively oxidized, characterized by dark red col-
oration, and waterlogged, characterized by near
black coloration.

Late Intermediate Period
Irrigation Systems Within the
Moche Valley

Irrigation agriculture within the Moche Valley
reached its maximum extent during the occu-

pation of the valley by people known as the
Chimu (Fig. 7). This state, governed from Chan
Chan its capital located within the Moche
Valley dominated the north coast during the
Late Intermediate Period. The beginnings of
this state date to about A.D. 900. By about A.D.
1300, the Chimu state had expanded north and
south to incorporate lands between the Jeque-
tepeque and Casma Valleys, thereby dominating
the area previously governed by the Moche
state (Donnan 1978:1; Mackey and Klymyshyn
1990:203-205; T Topic 1990:184-189). This
was apparently also the time of maximum ag-
ricultural expansion the time when the Chimu
implemented an aggressive program of canal
and field expansion within valleys under their
control. Motivated by an El Nino flood that ad-
versely impacted their land reclamation efforts,
the Chimu altered their strategy and expanded
their polity much further north and south to en-

Prehistoric Chimu Irrigation Systems

Chan Chan

[/ /j Modern cultivation

Figure 6. Map of the Three-Pampa area showing the major canals which functioned during Moche times (A.D.
100-600).

compass lands as far north as Tumbes and as
far south as the Chillon Valley (Donnan 1990:
267; Mackey 1987:121-122; Richardson et al.
1990:434-436; Rowe 1948; Shimada 1990:
313). Domination by the Chimu state ended in
A.D. 1470 as a result of defeat by the expanding
Inca empire.

Early Intermediate Period Moche canals un-
derlie some of the major channels that were
subsequently used by the Chimu; however, vir-
tually all of the prehistoric irrigation features
readily visible on the surface were originally
constructed by the Chimu. These include small
systems located well inland on either side of
the valley as well as the Three-Pampa area
an unusually large zone of ancient canals and
fields that extends from the edge of modern
cultivation toward the ocean (Figs. 1 and 2).
The Chimu were also responsible for the con-
ception and execution of the Chicama-Moche
Intervalley Canal, a massive undertaking to di-
vert water from the Chicama River 20 km to
the north and channel it onto the Three-Pampa
area (Kus 1972; Ortloff et al. 1982; T. Pozorski

1987:116; T. Pozorski and S. Pozorski 1982).
The Three-Pampa area, which consists of Pam-
pa Esperanza, Pampa Rio Seco, and Pampa
Huanchaco, is an integrated system of canals
and fields originally fed by two major canals
on the north side of the Moche River. The
Three-Pampa area as well as the Intervalley
Canal that was intended to supplement the wa-
ter supply for the Three-Pampa area are the
main focus of this study.

The Administration of Land Reclamation

In order to execute tasks as formidable as culti-
vation of the Three-Pampa area and construction
of the Chicama-Moche Intervalley Canal, the
Chimu built rural administrative centers (Keat-
inge 1974, 1980; Keatinge and Day 1973, 1974;
T. Pozorski 1987:1 14-1 17). Although these sites
also likely served to monitor maintenance of the
irrigation systems as well as production within
the fields, they were primarily established to
oversee initial canal and field construction. In

T. Pozorski and S. Pozorski

Cerro '

Campana /

Intervalley Canal

Par

4 km

[/ /j Modern Cultivation
|r-^~| Hill
|v^ u | Bluff

Prehistoric Cultivation

Figure 7. Map of the Moche Valley showing the extent of prehistoric irrigation outside of modern cultivation
during Chimu times (A.D. 1000-1300).

this capacity, the rural administrative centers rep-
resent expansion of the Chimu state onto previ-
ously unfarmed desert areas, and they are con-
sistently located in close association with canals
and field systems (T. Pozorski 1987:114-117).
Ironically, many of the canals and field systems
connected with rural administrative centers were
never fully operational.

Within the Moche-Chicama Valley area, four
rural administrative centers have been identified
and investigated to date. These centers are Que-
brada Katuay, located well inland on the north
side of the Moche Valley; El Milagro de San
Jose, located on Pampa Rio Seco (Fig. 2); Que-
brada del Oso, located some 3 km south of
modern cultivation in the Chicama Valley and
associated with the Chicama-Moche Intervalley
Canal; and Pampa Mocan, located 3.7 km north
of modern cultivation in the Chicama Valley

(Keatinge 1974; Kus 1972:99-102; T. Pozorski
1987:Fig. 1).

Challenges, Successes, Failures, and
Alternative Strategies

The Chimu faced distinct challenges as they ex-
panded the Moche Valley irrigation system far
beyond its previous limits, and especially as
they endeavored to draw water from the Chi-
cama River into the Moche system. These chal-
lenges are directly related to the fact that, once
the Chimu moved beyond land reclaimed in
Moche times, they were expanding the irriga-
tion system into areas not previously cultivated.
The topography, the nature of the local sub-
strate, and the lack of adequate water were for-

Prehistoric Chimu Irrigation Systems

O
Phase 1 architecture

.. Phase 2-3 architecture

Y A Modern cultivation

1 Velarde

2 Squier

3 Gran Chimu

4 Bandelier

5 Laberinto

Figure 8. Map of the Three-Pampa area showing the maximum extent of canal systems during preflood Chimu
times (A.D. 1000-1300).

midable obstacles. Once in place, prehistoric ir-
rigation systems were also impacted periodical-
ly by El Nino-related rainfall.

Topography

Paramount in the effort to fully reclaim the
Three-Pampa area was the extension of the Vi-
chansao Canal, the major canal that drew water
from the Moche River, so that water could be
transported to Pampas Rio Seco and Huanchaco
(Figs. 7 and 8). In doing this, the objective was
to incorporate the maximum amount of land
while also creating a functioning canal to pro-
vide water for this land. The projected route

was along the north edge of Pampa Esperanza,
then across Pampa Rio Seco a dry river chan-
nel, all the while maintaining sufficient eleva-
tion to provide water to Pampa Huanchaco, an
area of higher ground on the other side of Pam-
pa Rio Seco. The Chimu ran the Vichansao as
high as possible along the valley edge, creating
a channel with a remarkably shallow slope of
.0001. As the canal crossed Pampa Rio Seco,
the channel bottom ran at approximately the
surface level of the pampa for much of its
length. This was accomplished by building up
banks using soil scraped from the nearby sur-
face to create a channel at ground level, but
without any elevation of the canal bottom. Fur-
ther along, to cross lower portions of Pampa

T. Pozorski and S. Pozorski

Rio Seco and maintain elevation sufficient to
supply Pampa Huanchaco with water, a true aq-
ueduct was constructed, raising both the chan-
nel and banks above ground level.

Where the Vichansao was excavated into the
substrate or ran at ground level, occasional
abortive channels that take off "uphill" attest
to the difficulty of the builders' task, and also
suggest that Chimu engineering efforts were
characterized by trial and error. Nevertheless,
the Chimu were able to create a functioning ca-
nal that traversed varied terrain while maintain-
ing an extremely low slope in order to maxi-
mize the amount of land reclaimed. The Vi-
chansao, and lesser canals within the Three-
Pampa system, were functioning canals, as
indicated by laminar sediments and especially
oxidation. Although the degree of oxidation de-
creases toward the periphery of the system,
there is clear evidence of functioning canals all
the way out to Pampa Huanchaco. This is ample
testimony to the success of Chimu efforts to
extend the Moche Valley irrigation system far
beyond any previous limits.

Natural Substrate

In constructing the Vichansao canal, much of
the canal's channel was cut through a zone of
aeolian sand banked against Cerro Cabras.
Sand-filled channels attest to problems with lo-
cal sand blowing into the canal, and ample sand
in bank deposits documents successful efforts
to keep the channel open through regular clean-
ing. Such porous sand would also have allowed
much water loss through seepage until suffi-
cient finer particles silts and sands had ac-
cumulated to self-line the channel. There was
little effort to artificially line the channel as a
means of retarding seepage. Stone lining and,
rarely, adobe lining on the canal interiors was
regularly employed where the Vichansao
crossed Pampas Rio Seco and Huanchaco.
However, the channel bottom was not lined, and
sidewall lining apparently functioned more to
retain loose bank soils than to prevent seepage.
The same problems of substrate porosity and
blowing surface sand also impacted smaller
feeder canals and fields on the Three-Pampa
area. On Pampa Esperanza, which had been un-
der cultivation since the Early Intermediate Pe-
riod, field soils were silt-rich and less porous
near the surface, allowing for better moisture

retention. On the other two pampas, especially
Rio Seco, the substrate was very loose, con-
sisting of porous, coarse sand to gravel and cob-
bles. Ironically, although such soils make farm-
ing the surface difficult at first because so much
water is lost through evaporation and seepage,
they also provide near-ideal conditions for
drainage beneath the fields and canals. This pre-
vents the buildup of salts that can potentially
render fields useless.

Chicama-Moche Intervalley Canal

The Chicama-Moche Intervalley Canal ranks
among the most ambitious irrigation projects
ever attempted on the north coast. It represented
an effort to bring water from the Chicama River
across the 70-km-long canal route of rocky, un-
even desert to the Moche Valley (Fig. 9; T. Po-
zorski and S. Pozorski 1982:Fig. 1). Although
a few small areas of fields were laid out or con-
structed along its course between the two val-
leys, the Chicama-Moche Intervalley Canal
was apparently conceived of primarily as a
means to increase the amount of water available
for the Three-Pampa area within the Moche
Valley. Unfortunately, it also proved to be
among the most noteworthy engineering fiascos
ever documented archaeologically.

Evidence of oxidized sediments within the
main supply canal, the Vichansao, all the way
to Pampa Huanchaco reveals that the Chimu
had created a canal that was sufficiently well
engineered to reach the farthest limits of the
land they endeavored to bring under cultivation.
Nevertheless, the magnitude of oxidation within
the channel decreases markedly along its route
toward the periphery. This suggests that there
was rarely sufficient water to keep the farthest
reaches of the system under cultivation. To rem-
edy this, about A.D. 1 100 the Chimu embarked
on a labor-intensive effort to supplement the Vi-
chansao's flow and provide additional water to
the entire Three-Pampa area. Evidence of this
intent comes from the fact that the Chicama-
Moche Intervalley Canal path circles well
around the base of Cerro Cabras in order to feed
into the Vichansao at a point sufficiently up-
stream to allow access to Pampa Huanchaco
(Figs. 7 and 9). The system of smaller canals
(Fig. 9, Canals I and II) taking water from the
Vichansao to the fields was also redesigned at

Prehistoric Chimu Irrigation Systems

Y A Modern cultivation

Figure 9. Map of the Three-Pampa area showing the reconfiguration of the Moche Valley canal system in
anticipation of supplemental water from construction of the Chicama-Moche Intervalley Canal. The relationship of
the Great North Wall and Phase 2-3 architecture of Chan Chan to Canal II is also indicated.

about the same time in anticipation of the ad-
ditional water.

Much effort was expended on the Chicama-
Moche Intervalley Canal before it was finally
abandoned. At least one channel which in
places is quite shallow can be traced across
its entire intended route. The greatest elabora-
tion, however, is evident in the portion of the
canal north of the "divide" the highest point
topographically which the canal had to traverse
along its route between the Chicama and Moche
Valleys. This northern zone is an engineer's
nightmare because of the uneven terrain, a
seemingly unending series of quebradas and

rocky ridges descending from the Andean foot-
hills. When their first effort to create a func-
tioning canal failed, the Chimu tried again and
again, raising the channel each time in the hope
of attaining sufficient elevation to cross the di-
vide. This required tremendous effort, especial-
ly where the canal had to be supported against
bare bedrock. At several locations the Chimu
used fire to heat crack the stone, and then cut
through the bedrock of ridges that impeded the
canal's progress. Charcoal from these fires pro-
vided samples for radiocarbon dating (T. Po-
zorski 1987:113, Table 1). Some segments of
the canal were rebuilt as many as seven times,

T. Pozorski and S. Pozorski

with each successive segment requiring addi-
tional stone-lined terraces to shore up the down-
slope bank and support the channel.

Numerous excavations transecting the Chi-
cama-Moche Intervalley Canal channel were
made north of the divide in the vicinity of Que-
brada de Oso. This location was selected be-
cause canal construction was especially elabo-
rate there and a sizable expanse of fields and
smaller canals was also present. An exception-
ally large and long aqueduct had also been con-
structed in this area, across Quebrada del Oso.
This aqueduct was largely destroyed by El
Nino-related wash down the quebrada; how-
ever, this same El Nino destruction exposed a
cross section of the aqueduct that was cleaned
as part of the excavations of the Chicama-Mo-
che Intervalley Canal.

Despite claims of great Chimu engineering
skills (Kus 1972, 1984; Moseley 1992:260; Ort-
loff 1981, 1988, 1993, 1995; Ortloff etal. 1982,
1985), numerous excavations within the Chi-
cama-Moche Intervalley Canal yielded no ev-
idence that the canal had ever effectively car-
ried water (T. Pozorski 1987:116; T. Pozorski
and S. Pozorski 1982). Most significantly, there
was no evidence of oxidation in any of the
channels. Cuts transecting the canal occasion-
ally revealed bands of fine sand and silt; how-
ever, these lacked the laminar structure of mov-
ing water. These deposits are clearly the result
of standing water that periodically filled seg-
ments of the channels during El Nino rains.
Capture of standing water within segments of
the channel was facilitated by the undulating
slope of the canal that resulted from engineer-
ing error.

Smaller canals constructed to water the area
of fields near Quebrada del Oso likewise show
no evidence of use. Their construction is inter-
esting, however, because their intakes and chan-
nels were cut into the bedrock of ridges that
projected toward the fields. Where these ridges
ended, soils were mounded up to aqueduct the
channels into the fields. During the latest effort
to rebuild the canal, the intakes for these canals
were filled in, becoming part of the canal bank.
This ended all efforts to cultivate fields along
the Chicama-Moche Intervalley Canal route.

The entire 70-km length of the Chicama-Mo-
che Intervalley Canal was surveyed on foot as
well as mapped, and slope measurements were
made with a 1 -second theodolite. Problems that
Chimu engineers experienced in their efforts to

traverse the difficult terrain became readily ap-
parent during this careful study of the canal.
They clearly lacked the ability to topographi-
cally relate the elevation of the intake for the
Chicama-Moche Intervalley Canal within the
Chicama Valley to the elevation of the divide
the highest point the canal would traverse. The
result was a disastrously blind following of to-
pography "up and down" as the channel as-
cended and then descended quebradas. The
channel was also cut considerably uphill across
seemingly fiat, but actually ascending, surfaces.
Among the most notable examples of such en-
gineering flaws is a 13.8-km segment just south
of Quebada del Oso where the canal slope goes
uphill almost 70 m (T. Pozorski and S. Pozorski
1982:854-860). It would seem that once the
Chimu engineers left the Chicama Valley prop-
er, where they had used the cultivated valley
bottom and the river as their frames of refer-
ence, they were unable to lay out a functioning
canal with a downhill slope.

Impact of the El Nino of ca. A.D. 1300-1350

In approximately A.D. 1300-1350, an excep-
tionally strong El Nino event impacted the Pe-
ruvian north coast. The effect on the Moche
Valley irrigation system was considerable. Ca-
nal intakes along the river would likely have
been washed out, rendering canals inoperable
until repairs could be made. Damage to canals
was variable. In situations where El Nino wash
descended a hillside onto sandy pampa, small
canals were frequently totally washed away,
covered over, or filled in as the pampa sedi-
ments were rearranged by the action of the
swiftly moving water (Fig. 10). Canals and aq-
ueducts crossing quebradas were cut, and sub-
stantial segments were washed away by water
flowing perpendicular to the canal course. In
cases where floodwater flow paralleled the ca-
nal channel, additional water frequently entered
the channel. Flood water flowing within canals
that had initially been excavated into sandy sub-
strate caused considerable damage, often cut-
ting through the canal bottom and gouging out
a much deeper channel (Fig. 11). Floodgate
flowing within canals initially excavated into
rocky substrate caused less damage. Finer silt
and sand particles were washed from around
larger stones that came in contact with the

Prehistoric Chimu Irrigation Systems

Postflood channel

20 40 cm

Figure 10. Profile of a small north-south feeder canal parallel to and east of Canal II in a sandy area on Pampa
Esperanza. On the left are the remnants of the original channel, partially collapsed and then buried by El Nino wash
that hit the canal laterally. On the right is a reconstructed post-flood channel built over the flood sediments. This
second channel was never a functioning canal.

floodgate, and the surfaces of the stones were
scoured to a blue-gray color.

Such extensive damage made irrigation of
the Three-Pampa area impossible until repairs
could be made. Some efforts to reactivate the
system are readily evident in the archaeological
record. Where canals had been totally washed
away or obscured, new channels were built
(Fig. 10). Gouged-out segments were infilled to
approximately restore original slope (Fig. 11).
Segments of canals cut by perpendicularly
flowing water were also rebuilt. At times this
involved rerouting the channel above and
around the break to maintain the downhill slope
within a flood-enlarged gully or quebrada.

Instances where transverse cuts were repaired
were particularly instructive regarding the mag-
nitude of the El Nino event of ca. A.D. 1300-
1350. Characterization of this event as unusu-
ally severe reflects evidence from canal recon-
struction suggesting that no subsequent El Nino
had comparable impact. Survey data from the

Three-Pampa area reveal that sizable segments
of some canals were washed out. Some new
channels were built by the Chimu to reconstruct
canals at these locations. These new channels
are distinct from the earlier canal construction,
and have not been affected by later El Nino
activity. Other new channels have been tran-
sected by subsequent washes. None of the sub-
sequent damage, however, comes close in mag-
nitude to the swath cut by the A.D. 1300-1350
El Nino wash (see below, however, for a cau-
tionary note on this interpretation).

Within the Three-Pampa area, efforts to re-
pair the irrigation system were extensive; how-
ever, excavation within these channels revealed
that the reconstructed system was never effec-
tively used. Laminar sediments within channels
are minimal, and there is no evidence of the
associated oxidation indicative of significant
wetting and drying. Most channels pertaining to
this latest reconstruction are also considerably
smaller than preceding uses of the canal. These

Original channe

Original channel

Figure 11. Profile of Canal II near its north end. The original channel was a functional canal showing signs of
laminar deposits and oxidation. Then the center of this channel was gouged out by swiftly flowing El Nino wash off
Cerro Cabras that flowed down the route of Canal II. Water flowed around a large boulder, and then, as the flow
subsided, sediment was deposited. Finally, a reconstructed post-flood channel, which was never functional, was built
above the flood-deepened channel and its deposits.

T. Pozorski and S. Pozorski

less substantial, unused canals represent the fi-
nal, unsuccessful effort to irrigate the Three-
Pampa area. Clearly, reclamation of the Three-
Pampa area was no longer a priority for the
Chimu.

Despite efforts to reconstruct the system, the
Three-Pampa area was never effectively
brought back under cultivation after the A.D.
1300-1350 El Nino. The timing of this disaster
also coincides with the latest dates for the Chi-
cama-Moche Intervalley Canal, indicating that
its construction was halted at the same time.
The devastating effects of El Nino appear to
have been a catalyst that motivated the Chimu
to abandon both their unsuccessful efforts to
bring Chicama water to Moche canals and fields
as well as their previously successful efforts to
reclaim the relatively marginal Three-Pampa
area which the Chicama-Moche Intervalley Ca-
nal was supposed to have helped irrigate. Pos-
sibly to compensate for production lost due to
abandonment of the Three-Pampa area and for
labor wasted on the Intervalley Canal, the Chi-
mu changed their strategy and began to look
outside the Moche Valley for support.

Alternative Strategies

The sequence for canal construction and use on
the Three-Pampa area can be correlated with
the construction sequence for the compounds at
the Chimu capital of Chan Chan, immediately
south of Pampa Esperanza (Figs. 1 and 9). Gen-
erally, investigators agree that these compounds
served as palaces for the rulers of the Chimu
empire (Day 1980, 1982; Klymyshyn 1982; Ko-
lata 1982). Although there is disagreement
about the exact order of construction of the
compounds (Klymyshyn 1987:101-102; Kolata
1990; Topic and Moseley 1983:158-162), a
general three-phase construction has been de-
veloped by Kolata (1982) based on the shape
of adobe bricks used to build the major com-
pound walls. Of the ten monumental com-
pounds, four (Chayhuac, Uhle, Tello, and La-
berinto) make up Phase 1. Phase 2 consists of
the Gran Chimu compound and various asso-
ciated walls to the north of that compound, in-
cluding the Great North Wall that bounds the
south side of Pampa Esperanza (Fig. 9). Phase
3 consists of the five remaining compounds
(Squier, Velarde, Bandelier, Tschudi, and Riv-
ero). Since the publication of Kolata's original

sequence, many other investigators, including
Kolata himself, have proposed more detailed
construction sequences based on analyses of ar-
chitectural elements within the compounds such
as audencia shape, burial platform configura-
tion, and entry courts, as well as associated ce-
ramics (Klymyshyn 1987:101-102; Kolata
1990; Topic and Moseley 1983:158-162). All
of these sequences, however, represent only mi-
nor variations on Kolata's original 1982 se-
quence and have little bearing on the overall
relationship between the monumental com-
pounds and the Three-Pampa irrigation area.
Therefore, for the purposes of this discussion,
we will follow the original Kolata sequence.

During the construction of the Phase 1 Chan
Chan compounds, when the site was in its ear-
lier stages of growth, the irrigation system
reached its maximum extent. Effecting their ag-
ricultural expansionist policies through rural ad-
ministrative centers, the Chimu attempted to re-
claim inland areas on both sides of the valley,
incorporated the entire Three-Pampa area, un-
dertook construction of the Chicama-Moche In-
tervalley Canal, and expanded Chicama Valley
irrigation systems beyond modern limits. Ar-
chaeological data indicate that use of the ex-
panded Moche Valley irrigation system was
abruptly interrupted between A.D. 1300 and
1350 by a devastating El Nino event. Despite
efforts to reconstruct the system, reclamation of
the more marginal zones of the Moche Valley
agricultural system was effectively curtailed at
about this time, and work on the Chicama-Mo-
che Intervalley canal also ceased. The same El
Nino event likely caused similar damage in oth-
er north and north-central coast valleys.

Chan Chan, however, continued to develop
after the flood. Five compounds (Phases 2 and
3), comprising about half the area of Chan
Chan, were built after the irrigation system had
shrunk to approximately its modern limits. The
key to this dating is the relationship between
Canal II on Pampa Esperanza and the Great
North Wall which is part of the Phase 2 con-
struction at Chan Chan (Figs. 9 and 12). Canal
II, which was part of the reworking of the
Three-Pampa irrigation system in anticipation
of water from the Intervalley Canal, is one of
the latest canals to be built on Pampa Esperanza
(Fig. 9). This canal contains sediment and oxi-
dation associated with its original use plus de-
posits associated with the A.D. 1300-1350 flood
within its channel (Fig. 12). The Great North

Prehistoric Chimu Irrigation Systems

20 40 cm

Figure 12. Profile of Canal II near its south end. The original channel was a functional canal complete with
laminar deposits and oxidation. Subsequently the El Nino wash entered the channel, scouring out a small depression
and leaving flood-borne deposits. Finally, a major east-west segment of the Great North Wall of Chan Chan, here
composed primarily of adobe, was constructed over both the original channel and the flood sediments within this
portion of the Canal II.

Wall, which is part of the Phase II construction
of Chan Chan, was clearly built over Canal II.
Thus, at least one-half of the visible compounds
at Chan Chan postdate the time when the
Three-Pampa area was most effectively irrigat-
ed. The minor, and largely unsuccessful, efforts
at canal reconstruction on the Three-Pampa
area after the A.D. 1300-1350 flood could par-
tially overlap with the building and use of the
Phase 2 architecture of Chan Chan, but are un-
likely to date any later.

The devastating El Nino flood that curtailed
reclamation efforts was likely a key factor in
changing Chimu strategy. Rather than expend-
ing excessive labor to maintain fields in mar-
ginal lands, the Chimu apparently formed ad-
ditional military units and set out to expand
their domain into more northern and southern
lands from which tribute could be extracted.
Strategically, this was an optimum time to take
advantage of rival polities that had been weak-
ened by the El Nino disaster, especially farther
north, where the impact was likely more severe.

This second, more far-reaching phase of Chimu
expansion was likely motivated not so much by
the desire for agricultural products as by the
desire to gain access to and control over the
production of artisan goods, especially the met-
alworking that had been so successfully con-
trolled from the Lambayeque area (Shimada
1982:178-179; T. Topic 1990). Within the ca.
1 50-year span between the flood of A.D. 1 300-
1350 and their defeat by the Inca, the Chimu
quadrupled the area they controlled.

This example from the Moche Valley and
surrounding north coast areas dominated by the
Chimu reveals some surprises regarding state
development in the Andean area. Clearly, irri-
gation agriculture provided the subsistence base
that allowed a certain level of political devel-
opment by the Chimii. It is not the case, how-
ever, that the maximum extent of land recla-
mation for agriculture coincided with the max-
imum extent of state development and Chimii
polity expansion. During the time between ca.
A.D. 1050 and the flood of A.D. 1300-1350,

T. Pozorski and S. Pozorski

when the Chimu invested so much labor in ca-
nal and field-system construction, their political
control extended over relatively few valleys.
Subsequently, as a result of a distinct strategy
that focused on more effective control and use
of human labor and craft production, the Chimu
emerged as an empire spanning 1,300 km of
coastal Peru and rivaling the Incas.

Detecting El Nino Evidence in the
Archaeological Record:
A Cautionary Note

It is clear that evidence of past El Nino events
can be detected in the archaeological record of
the desert coast of Peru (Moseley 1992:215,
254; T. Pozorski 1987:113; Shimada 1982:180).
The stronger the El Nino event, the more likely
it is to have a direct impact on archaeological
remains. Such impacts can be detected as
washed-out areas or distinct laminar deposits in
irrigation features, as shown in this paper, or in
association with architectural features (Uceda
and Canziani 1993).

Detecting individual El Nino events at single
archaeological sites is one thing; however, con-
necting those events with apparently similar-
looking events at other sites and areas, either
within the same valley or in other valleys, is a
much more difficult task. The ability to inter-
connect El Nino events over increasingly large
areas along the coast of Peru would be a pow-
erful chronological tool that could provide dat-
ing precision unmatched by any other dating
means available in Peru. Furthermore, the im-
pact of strong El Nino events could also pro-
vide potential explanations for cultural changes
in the archaeological past (von Hagen and Mor-
ris 1998:22).

There are two main problems with El Nino
correlation in the archaeological record. The
first problem is chronology. Precise dating is
essential for correlating El Nino events, wheth-
er one is connecting areas or sites within a val-
ley or across many valleys. In the present dis-
cussion, it is postulated that a major El Nino
hit the Moche Valley irrigation system around
A.D. 1300-1350, resulting in major repercus-
sions on Chimu political strategy. However,
some authors have dated this flood two centu-
ries earlier, to A.D. 1100 (Moseley 1992:254;
Nials et al. 1979). Furthermore, this Moche Val-

ley flood has been correlated with an A.D. 1 100
flood that occurred in the Lambayeque region
(Moseley 1992:252-254; Richardson 1994:
143). We believe that the stratigraphic evidence
correlating the flood with the construction se-
quence of Chan Chan supports an A.D. 1300-
1350 date for the Moche Valley El Nino and
that it represents an event distinct from the
Lambayeque A.D. 1100 El Nino. It is apparent,
however, that there is substantial disagreement
on this correlation.

This single example points out the chrono-
logical problem with El Nino correlation. Here
are two El Nino events, separated in time by
two centuries, that are nevertheless the source
of chronological controversy. The problem can
only get more complicated as one deals with El
Nino events more closely spaced or more dis-
tant in time. Given that major El Nino events
affect much of the north and central Peruvian
coast at least two or more times per century,
and given the relative grossness of dating meth-
ods currently available, archaeologists will be
hard-pressed to distinguish and date El Ninos
that occur within 50 years of one another, let
alone within 15 years, as is the case with the
recent 1983 and 1998 floods.

A second, potentially even more difficult
problem is the spatial correlation of strong El
Nino events. We were able to correlate the im-
pact of a strong El Nino event over a fairly
large area of land by carefully studying strati-
graphic relationships of linear features (canals,
walls, roads) that intersect in certain places.
Most archaeological contexts are not character-
ized by such linear features, instead involving
sites or features that are separated spatially by
many kilometers. In some instances, a fairly
strong case can be made for correlating a single
El Nino between two sites. For example, in the
Casma Valley, a major El Nino hit the site of
Cerro Sechin around 1200 B.C. Here, a recon-
structed floor built on top of a filled-in corridor
behind the main mound trapped a pool of water
that softened the clay floor, which was then trod
upon by several individuals (Fuchs 1997:150-
152). Some 5 km away, at the site of Pampa de
las Llamas-Moxeke, what were likely the same
El Nino waters fell, damaging portions of friez-
es on the main mound (Huaca A) as well as
wetting the floor of an adjacent enclosure upon
which several individuals trod, similar to the
Cerro Sechin case (Fig. 13).

The Casma Valley case just described is en-

Prehistoric Chimu Irrigation Systems

Figure 13. Human footprints on the floor of an enclosure adjacent to Huaca A at the Initial Period site of Pampa
de las Llamas-Moxeke in the Casma Valley. The enclosure floor was wetted heavily by an El Nino event dated to
about 1200 B.C.

tirely plausible, given the available stratigraphic
and radiocarbon evidence, but is by no means
conclusively proven. It is often assumed that
major El Nino events will bring rains that will
more or less uniformly blanket the entire area
adjacent to the ocean zone that is penetrated by
the Ecuadorian Countercurrent. Observations of
rainfall patterns of the 1983 and the 1998 El
Ninos indicate otherwise. Along the north and
north-central coast, some valleys were hit hard-
er than others. Most rainfall came down well
inland from the coastline, between elevations of
1000 and 1500 m. Geologically, riverbeds were
quite changed as river channels were deepened,
substantially widened, and scoured of vegeta-
tion. This was quite evident during the 1998
event for every valley between Chicama and
Huarmey.

Archaeological sites and modern settlements,
however, were more variably affected. In the
Casma Valley, the Late Intermediate Period
adobe mound site of Sechin Bajo was complete-
ly washed away by the swollen Sechin River.
One kilometer away, the Initial Period site of

Sechin Alto, situated a few hundred meters
south of the Sechin River, was only minimally
affected by rainfall that resulted in a few thin
patches of silt that settled from small puddles
of water. In the modern town of Casma, there
were episodes of rainfall during March 1998.
During one particularly heavy downpour that
lasted some two hours, the south part of town
was drenched by several centimeters of rain,
whereas the north part of town, 0.5 km away,
received less than 1 cm of rain. This uneven
distribution of rainfall during El Nino events
should not be surprising to anyone who has ex-
perienced rainfall, and there is no reason to as-
sume that El Nino rainfall patterns should be
any different.

The main point of this discussion is to high-
light the difficulties of El Nino correlation.
There are problems associated with both the
temporal and spatial correlations of El Nino
events documented from different areas of
coastal Peru. El Nino events that leave abun-
dant evidence in several places can potentially
reveal important chronological and cultural in-

T. Pozorski and S. Pozorski

formation, yet careful study is needed to make
precise correlations. A more difficult task is the
correlation of El Ninos that leave behind only
widely scattered pieces of evidence. What ap-
pears to be a major El Nino event in one valley
may leave only minimal or no evidence in an-
other valley or even in another part of the same
valley. The absence of evidence of an El Nino
event at a particular site does not mean that
such an event did not happen. All this means is
that the particular El Nino event did not happen
to affect the one site in question. What remains
a challenge to both archaeologists and geomor-
phologists alike is the documentation and cor-
relation of El Nino events and their physical
and cultural effects. This can only be done
through a long series of careful, detailed studies
that will need to be carried out over the next
few decades.

Acknowledgments. Funding for the Programa
Riego Antiguo investigation of prehistoric irri-
gation systems was provided by National Sci-
ence Foundation grants BNS76-24538 and
BNS77-24901. Permission to excavate was
granted by the Peruvian Institute Nacional de
Cultura. The authors thank Michael E. Moseley
for the opportunity to serve as codirectors of
the project; to Eric E. Deeds for his hard work
as part of the project, particularly in survey,
mapping, and the recognition of archaeological
evidence of El Nino; and to geologist Fred
Nials for his help in interpreting both cultural
and natural soils associated with irrigation fea-
tures.

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El Nino, Early Peruvian Civilization, and Human Agency:
Some Thoughts from the Lurin Valley

Richard L. Burger

The role of El Nino in the rise and fall of early
Andean civilizations has attracted increasing at-
tention over the past two decades as more has
become known about the role of climate change
in human history. It is no coincidence that this
greater sensitivity to climate change in the ar-
chaeological past has emerged as we have be-
come increasingly anxious about global warm-
ing and the way it could affect our future. As
science has focused more intently on global cli-
matic change, new methods and theories have
been developed that allow us to reconstruct past
climates and to appreciate the degree of vari-
ability that has existed in the Holocene climate,
of which the El Nino phenomenon is but one
small piece.

The past two decades also saw two major El
Nino events. As a consequence, many archae-
ologists working in Peru have experienced, ei-
ther firsthand or through media coverage, the
devastation that a major El Nino event can pro-
duce. By contrast, in 1980, only the most senior
archaeologists had personally experienced a
major Nino event, and most academics had to
rely on accounts of the 1925 El Nino to imagine
what its effects were like. Thus, historical hap-
penstance has placed scholars in a situation
where there are now both personal experience
and the academic predisposition to take El Nino
seriously in the archaeological modeling of civ-
ilizational trajectories in the distant past. Such
was not always the case. In the late 1960s, for
example, both Edward Lanning (1967) and Luis
Lumbreras (1969) found it possible to write

syntheses of Andean prehistory with barely a
reference to the El Nino phenomenon, and the
immediately previous generation of scholars,
such as Bushnell (1957) and Bennett and Bird
(1960), ignored El Nino entirely. Such an ap-
proach has now been largely supplanted, as ev-
idenced by the work of Michael E. Moseley
(1992) and James Richardson III (1994), in
which El Nino figures prominently as a possible
contributing factor to the emergence, expansion,
reorganization, and demise of multiple Peruvian
cultures, including those of Chavfn, Moche, and
Chimu.

Recent archaeological literature on the pos-
sible effect of El Nino on Andean prehistory
has usually focused on the role of El Nino in
the evolution of Andean civilization. A classic
example was a 1981 article by David Wilson,
in which he posited the El Nino phenomenon
as a limiting factor in the development of an
early maritime civilization in the Central Andes
because of the unpredictable but radical reduc-
tion in maritime carrying capacity along the
coast during major El Nino events. In a more
recent 1999 synthesis, Wilson (1999:352-356)
updated his earlier argument and suggested that
the stresses caused by El Nino could help ex-
plain how a primarily maritime-oriented people
might accept agriculture as an alternative strat-
egy, thus creating the conditions for the emer-
gence of complex society. In the models pro-
posed by Wilson and others, El Nino is seen as
shaping a long-term evolutionary trajectory as
cultures become adapted to their environmental

El Nino, Early Peruvian Civilization, and Human Agency

conditions; the role of human actors and their
strategies is seen as secondary to larger evolu-
tionary processes. Not surprisingly, such mod-
els have been criticized as treating humans as
fundamentally passive and as constructing so-
cial change merely as a process of reacting to
natural phenomena, such as natural disasters or
long-term changes in climate. Although such
models have merit, it also is important to con-
sider whether the peoples of pre-Hispanic Peru
anticipated the dangers posed by El Nino events
and whether they were able to develop strate-
gies to mitigate them. In adopting this second
approach, we recognize that human agency
played an important role in determining cultural
stability and change in the past, just as it does
in the present.

In the modern world, major disasters are
most successfully dealt with at the level of the
nation-state or international community. For ex-
ample, 90% of the $14 billion in aid to the vic-
tims of the 1994 California earthquake came
from the federal government of the United
States rather than from local or state sources,
and in Honduras, virtually all aid to alleviate
the devastation wreaked by Hurricane Mitch
has come from governmental and charitable
sources outside of Central America (Davis
1998). But what disaster strategies were em-
ployed prior to the emergence of such over-
arching social and political structures?

Possible Pre-Hispanic Responses to
El Nino Events in the Central
Andes

In the absence of state-based systems, one way
of dealing with recurring environmental disrup-
tions such as El Nino is for families or small
social units to develop links with distant com-
munities that are less likely to be affected by
the environmental perturbation. In the case of
the northern and central coast of Peru, for ex-
ample, longstanding links with adjacent high-
land communities would have facilitated a pre-
historic alternative to current disaster relief,
perhaps under the rubric of fictive kinship ob-
ligations or gift exchange. At the 1982 confer-
ence on Early Monumental Architecture at
Dumbarton Oaks, I suggested that in combina-
tion with the dietary needs of highlanders (e.g.,
for iodine and salt), the danger presented by El

Nino events would have favored the establish-
ment of ties between highland and coastal
groups that could be mobilized in times of di-
saster. Llama caravans could have brought
highland agricultural produce down to com-
munities where an El Nino had devastated both
the year's crops and maritime productivity
(Burger 1985:276).

A modern version of such a strategy was
mentioned in Robert Murphy's description of
the 1925 El Nino, in which food shortages on
the central coast were solved by "mutton on the
hoof" driven down from the high grasslands
(puna) and by pack trains of llamas, horses, and
burros from the highland valleys carrying po-
tatoes and other foodstuffs (Murphy 1926:46).
The continued viability of agricultural systems
in the northern highlands during the last two
major Nino events supports the plausibility of
this idea.

Moreover, recent research by Ruth Shady
(1997) at Caral in the Supe Valley and by She-
lia and Thomas Pozorski (1992) at Huaynuna
and Pampa de las Llamas in Casma has rein-
forced our appreciation of the Late Preceramic
and Initial Period links between the highland
societies involved in the Kotosh Religious Tra-
dition and their contemporaries in centers on
the coast. Unfortunately, the hypothesis of high-
land economic assistance to coastal settlement
during El Nino events has yet to be tested on a
microlevel by studying examples of a Late Pre-
ceramic or Initial Period center that coped with
an El Nino event. It would be fascinating to
know if the survival strategy of such a site was
characterized by refuse that included a sharp
increase in the amounts of highland meat and
agricultural produce to compensate for the dis-
ruption of marine and lower-valley agricultural
resources.

In Andean archaeology, one of the rare in-
stances of a local-level analysis of a prehistoric
community struggling to deal with an El Nino
event is the study of two Chimu settlements in
the Casma Valley by Jerry Moore (1991).
Moore not only used archaeology to document
the occurrence of a fourteenth century A.D. El
Nino event, he also explored some of the cul-
tural responses to it. He concluded that imme-
diately following a powerful El Nino, the Chi-
mu state established a complex of ridged fields
in order to reclaim waterlogged soils, and an
adjacent community to house agricultural work-
ers. This subsistence system was apparently

R. L. Burger

maintained for no more than a few years, while
the normal farming system was restored, after
which time the site was abandoned. According
to Moore, by shifting to the cultivation of fields
that were not irrigated, along with exploiting El
Nino-resistant species of shellfish, it was pos-
sible to support the continued occupation of the
Casma Valley and its administrative center at
Manchan despite the devastation wreaked by a
major El Nino event. This case is particularly
interesting because it illustrates how one pre-
Hispanic group consciously combined two of
many possible strategies in order to cope with
the conditions created by El Nino. In this case,
the rains from El Nino may have created the
opportunity for successful dry-farming in this
section of the normally arid coast.

Given recent history, it should not be news
to anyone that El Ninos produce occasional op-
portunities as well as serious problems. One has
only to recall the scandal that occurred during
the 1982-1983 El Nino, when several high-
ranking military men were accused of using
army cargo planes to fly cattle down from Pan-
ama to graze on the vast pasturelands that had
appeared in Peru's Sechura Desert. The appear-
ance of more robust lomas vegetation, the mi-
gration of new kinds of fish, the short-term
availability of new land for rainfall farming,
and the sprouting of new pastures may be only
small consolation when weighed against the
enormous losses occasioned by an El Nino
event, but such factors may have been crucial
for crafting locally based survival strategies in
pre-Hispanic times. Additional studies along the
lines of the Casma research should yield greater
insight into the significance of these alterna-
tives. It should be noted that the strategy pos-
ited by Moore for Casma involved the inter-
vention of state institutions, which were absent
in much earlier prehistoric times.

Pre-Hispanic Human Agency,

El Nino, and the Manchay Culture

Thus far I have explored some of the possible
short-term responses to the effects of El Nino
events in the pre-Hispanic Central Andes. How-
ever, as geographer Kenneth Hewitt has ob-
served, "Most natural disasters are character-
istic rather than accidental features of the places
and societies where they occur" (Davis 1998:

52). In the longer-term perspective, humans can
be considered agents that, with the accumulated
knowledge of their landscape, either learn to
anticipate potential disasters and avoid them or
choose to ignore the dangers and place them-
selves in harm's way. Mike Davis's book, The
Ecology of Fear (1998), provides an excellent
illustration of this perspective. He shows how
flawed human decisions acted to turn tectonic
and climatic forces into major dangers in the
course of human settlement in southern Cali-
fornia.

Following in this line of thought, I want to
consider here whether the coastal societies of
Peru during the second millennium B.C. (known
as the Initial Period) perceived the possible
threat posed by the El Nino phenomenon, and
if they did, what actions they may have taken
to protect themselves. In the Central Andes, this
period of time is of particular interest to those
interested in the relationship between El Nino
and the appearance of complex societies be-
cause it was the time of the emergence of the
region's earliest civilizations. Among the ac-
complishments of the coastal cultures of the Ini-
tial Period were the creation of abundant mon-
umental architecture, the production of sophis-
ticated public art, breakthroughs in metallurgi-
cal techniques, and the building of extensive
irrigation systems. This Initial Period culture,
characterized by massive civic-ceremonial cen-
ters with a U-shaped layout, extended along the
central coast from Chancay Valley on the north
to Lurin Valley on the south. Investigations of
these U-shaped centers of Manchay culture by
myself and Lucy Salazar (Burger 1992:60-75;
cf. Silva and Garcia 1997) have focused on the
southernmost of these valleys, which is located
immediately south of contemporary Lima, and
the following commentary is based on our on-
going research.

During the second millennium B.C., the pop-
ulation in the lower Lurin Valley gradually in-
creased, as reflected in the founding of civic-
ceremonial centers that served as the focus of
small-scale social units. Only one such center
is known to have existed in 1800 B.C., but by
1000 B.C., at least six such centers appear to
have been functioning in the lower valley, and
several more in the middle valley (Fig. 1).
These centers appear to have been autonomous
and were not organized by an overarching state
apparatus; the latter appeared only much later
in the prehistory of the central coast. The pop-

El Nino, Early Peruvian Civilization, and Human Agency

CENTROS DBL PBRIODO INIC1AI

VALLK OB LUMIM

Figure 1. The location of Initial Period U-shaped pyramid complexes in the lower Lurin Valley, Peru. (Map
drawn by Bernadino Ojeda.)

R. L. Burger

ulation supporting these centers survived on a
mixed subsistence system based on irrigation
farming of crops such as squash, peanuts,
beans, red pepper, guava, pacae, and lucuma, as
well as yet unidentified tubers (sweet potato?),
manioc, and a small amount of maize. These
domesticated crops were supplemented by the
collection of wild plants, the acquisition of fish
and mollusks from the Pacific shore, and the
hunting of deer, camelids, vizcachas, and birds
from nearby lomas and riverine environments
(Benfer and Meadors 2002; Burger and Salazar-
Burger 1991; Umlauf 2002).

The largest of the valley's centers, Mina Per-
dida, was occupied for about a thousand years
(calibrated C14 years) without evidence of hi-
atus or abandonment (Burger and Salazar-Bur-
ger 1998, 2002). If one accepts the proposition
that the pattern of El Nino events was estab-
lished by 5,800 years ago (Rollins et al. 1986),
the Manchay culture in Lurin presents an ex-
ample of cultural continuity and resilience for
at least ten centuries in the face of the major El
Nino events that must have occurred during this
time. Even if one accepts that El Nino had a
longer recurrence interval until 3200-2800 cal
B.P. (Sandweiss et al. 2001), the centers of the
Manchay culture would still have experienced
numerous major El Nino events, a fact con-
firmed by the research I shall describe below.

Considering the dangers posed by El Nino
events, the choice of location for Lurin's
U-shaped centers was not auspicious; in fact, to
use Mike Davis's phrase, it could be said that
the groups living in the lower Lurin Valley
chose to place their centers in harm's way. The
public complexes were generally built at the
mouth of deeply cut ravines (quebradas). These
quebradas were normally bone dry, but they
sometimes carry water during El Nifios. Such
locations may have been chosen because they
provided expanses of relatively level land ad-
jacent to the valuable irrigated bottomlands of
the valley. Moreover, the nearby rocky ravines
and barren valley sides offered ample building
materials, including stone blocks and lenses of
clay suitable for mortar and adobes. Unfortu-
nately for the inhabitants of these centers, the
loose rock, rubble, and earth in these quebra-
das, which make such good building materials
under normal circumstances, are incorporated
into landslides and debris flows when heavy
rainfalls occur in the lower Lurin Valley during
major El Nino events.

Manchay Bajo and Its Monumental Wall

Judging from the results of fieldwork in 1998
and 1999 by the Yale University Lurin Valley
Archaeological Project at Manchay Bajo, the
Initial Period occupants of Lurin not only were
aware of the danger posed by an El Nino event,
they consciously worked to protect themselves
against potential disasters. Manchay Bajo
(PV48-147) is located in the lower valley, 12
km inland from the Pacific, at 140 m above sea
level (masl). In contrast to the U-shaped com-
plexes of Mina Perdida and Cardal, Manchay
Bajo is on the northern bank of the Lurin River,
only 800 m from the current course of the river.

Manchay Bajo is, in most respects, a typical
U-shaped complex. The archaeological com-
plex is dominated by a terraced, flat-topped
central pyramid (Fig. 2), and the site is oriented
to the northeast. The pyramid, found at the apex
of the U, measures 100 X 75 m at its base and
rises 13m above the current level of the valley
floor. Two elongated lateral mounds, one of
which is attached to the main pyramid, flank a
central plaza that is 3 hectares in area (Fig. 3).
Although lower than the main mound, the lat-
eral mounds are of considerable size, with
heights of 1 1 m and 8 m, respectively. The area
of the site, roughly 20 hectares, and the scale
of the monumental architecture are slightly
larger than at Cardal, which is located 1.7 km
away on the other side of the river. The exca-
vations at Manchay Bajo revealed a long his-
tory of construction at the center that included
a minimum of nine superimposed central stair-
ways, three superimposed atria, each with mul-
tiple renovations, and at least nine major build-
ing episodes. Thus, the large public construc-
tions seen today were the result of repeated
constructions that spanned at least six centuries.

Most of the ceramics associated with the
monumental constructions date to the late Initial
Period (approximately 1200-800 cal. B.C.). This
is consistent with an AMS measurement of
3010 60 (AA 3442), which, when calibrated,
has a 2a range of 1404-1052 B.C.; the specimen
tested comes from a fiber bag (shicra) used to
hold stone in the fill covering the site's middle
atrium. Since this measurement dates the clos-
ing of this structure, and since an even older
atrium exists below this one, Manchay Bajo
must have been founded significantly before
this time. Although most of the construction ep-
isodes at Manchay Bajo date to the late Initial

El Nino, Early Peruvian Civilization, and Human Agency

Figure 2. Central mound at Manchay Bajo, Lurin Valley, during the 1998 excavations on the summit terraces.
Modern agricultural constructions visible on the lower left are encroaching on the archaeological site. (Photograph
by Richard L. Burger.)

Period, the uppermost levels yielded a distinc-
tive ceramic assemblage that dates to the Early
Horizon; no hiatus is indicated (Fig. 4). The
preliminary stylistic interpretation of the pot-
tery is consistent with two AMS C14 measure-
ments of 2560 50 B.P. (Beta- 122683) and
2600 50 (AA 34441) from the final period
of construction which, when calibrated, pro-
duced a 2a range between 815-525 B.C. and
894-539 B.C., respectively. Thus, the available
evidence indicates that whereas Manchay Bajo
was contemporary with Cardal and Mina Per-
dida during the final centuries of the Initial Pe-
riod, it continued to function as a civic-cere-
monial center for a century or more after the
others were abandoned (Fig. 5). Manchay Bajo
is situated at the mouth of two quebradas that
were incised into the Andean spur separating
Lurin from the Rimac drainage (Fig. 6). The
larger of these, known today as the Quebrada
Manchay, is a dry tributary valley located to
the north of Manchay Bajo. It is separated from
the valley through which the Lurin River flows
by a massive rocky spur (246 masl). The small-

er of the two quebradas is located to the north-
west of the site and is unnamed; it extends only
for about a kilometer. The Quebrada Manchay
was used as a natural corridor between the Lu-
rin and Rimac in prehistoric times, and this
route continues to be used today despite the
poor state of the unpaved road. Given the nature
of the topography and Manchay Bajo's location,
a major El Nino could have triggered landslides
through the large Quebrada Manchay, which
would have buried the site's central plaza in
stone rubble. A debris flow from the shorter,
unnamed lateral quebrada would have had a
strong effect on the western lateral platform of
Manchay Bajo. Undeterred debris flows from
either or both quebradas would have had the
greatest impact on the residential zone covering
the flatland to the north and northwest of the
public architecture.

The potential danger posed for prehistoric
occupations and public spaces by landslides and
debris flows from the small lateral quebrada
was highlighted by the excavations at the site
of Pampa Chica by archaeologists from the

R. L. Burger

MAPA ARQUEOLOGICO
MANCHAY BAJO
PVA8_147

Figure 3. Topographic map of the Manchay Bajo complex indicating the location of excavation units and the
monumental wall extending along the western and northern extremes of the site. (Map drawn by Bernadino Ojeda.)

Pontificia Universidad Catolica (PUC), Lima,
under the direction of Jalh Dulanto as part of
the Proyecto Arqueologico Tablada de Lurin,
directed by Krzysztof Makowski. Pampa Chica,

a small site located up the smaller of the two
quebradas at 180 masl, had been covered by
landslides. Occupied between the Early Hori-
zon and the Middle Horizon, investigations at

El Nino, Early Peruvian Civilization, and Human Agency

Figure 4. Incised fragment of a polished blackware vessel depicting a frontal face with two large fangs. This
sherd from Manchay Bajo illustrates the pottery associated with the final phase of construction at the U-shaped
pyramid complex. (Photograph by Richard L. Burger.)

the site found evidence of repeated debris flows
in prehistoric times (Dulanto et al. 2002).

In addition to the danger posed to Manchay
Bajo by flash floods and debris flows coming
out of the Quebrada Manchay and the smaller
lateral quebrada, a threat also was posed by a
138-m-high rocky outcrop (278 masl) immedi-
ately to the west of the main mound (Fig. 7). It
is covered with large stone boulders and loose
stone rubble, and this unconsolidated material
would have become unstable during an El Nino
event or an earthquake.

Prior to 1998, no topographic map of the en-
tire archaeological site of Manchay Bajo exist-
ed. However, Harry Scheele (1970:179-190)
had carried out test excavations at the site in
1 966 and produced a sketch map of the central

portion of the site. In subsequent years, many
visitors, including Alberto Bueno Mendoza,
members of the PUC Pampa Chicha team, and
me, have examined Mancho Bajo and been in-
trigued by a large wall that rings its western and
northern perimeter. Our investigations included
a detailed mapping of the entire site, and it was
determined that the massive wall begins at a
rocky outcrop near the southwest corner of the
northwest lateral platform and runs in a north-
erly direction for some 460 m. The wall then
turns eastward and runs for another 240 m (see
Fig. 3). Unfortunately, its final section was de-
stroyed by the construction of a modern road,
but it appears that the eastern end terminated
45 m away, at the large rocky outcrop that de-
fines the eastern edge of the Quebrada Man-

R. L. Burger

700

800

900

1000

1100

1200

13CC

Cardal

Mina
Perdida

Manchay
Bajo

Figure 5. Radiocarbon measurements from the three U-shaped complexes excavated in the Lurin Valley dem-
onstrate both the general contemporaneity of the centers and the continued occupation of Manchay Bajo after the
abandonment of the other two sites. (Chart by George Lau.)

chay. Both of the two extremes of the monu-
mental wall appear to have been engaged with
natural topographic features anchoring this re-
markable cultural feature to the landscape. The
total length of the original wall is estimated at
745 m.

During the mapping and surface survey in
1998, masonry retaining walls could be seen at
various points along both the north-south and
east- west segments of the perimetric wall. In
those sections where it has been exposed, the
original wall can be seen to be double-faced,
with a core of unconsolidated stone, gravel, and
earth. In both segments there is evidence of at
least one and in some cases two renovations of
the wall; this was done by adding new walls
separated from the previous walls by a layer of
fill. These additions would have widened the
wall substantially while reducing strain on the
walls incorporated into the core. This same pat-
tern of growth was determined for the terrace
walls on the central pyramid of the Manchay
Bajo complex. Like the Manchay Bajo's plat-
form constructions, construction of the original

monumental wall and its subsequent renovation
were carried out with medium-sized blocks of
roughly dressed stone from the nearby slopes
(Fig. 8). Clay mortar was used at the junctures,
but during the surface reconnaissance, no sur-
viving evidence of surface plastering was en-
countered. The width and height of the wall
varied, and in many places its limits are com-
pletely hidden under collapsed or accumulated
material. Nevertheless, the topographic map
suggested that the north-south segment had an
average width of about 12.5 m and an average
height of at least 5 m, and portions of the east-
west segment were still more massive. Surface
ceramics were encountered at various points on
the summit of the wall; they were particularly
common near its eastern end because of distur-
bance from the modern construction of a small
chapel on top of the wall. Based on vessel
forms and decoration, all of the pottery can be
dated to the late Initial Period. It included nu-
merous shallow open bowls and neckless ollas.
Some of the former had the vessel interior dec-
orated with broad incisions. The surface ceram-

El Nino, Early Peruvian Civilization, and Human Agency

Figure 6. Aerial photograph of Manchay Complex taken in 1945 displaying the relation of the pyramid complex
to the two ravines or quebradas (on the viewer's left and upper left) and the Lurin River (on the viewer's right). The
monumental wall can be seen anchored to two rocky outcrops to the west and north of the site. (Courtesy of Servicio
Aereofotografico Nacional, Lima.)

ics found on the wall in 1998 were indistin-
guishable from those found in the excavations
of the main mound at Manchay Bajo that same
year. No later ceramics were on or near the
wall. Based on the masonry style of the surface
architecture and the ceramic evidence, a prelim-
inary conclusion was reached that the monu-
mental wall had been constructed during the
Initial Period and was roughly contemporary
with the adjacent U-shaped public architecture.
Following the mapping and study of the
monumental wall just described, we encoun-
tered another masonry feature at the foot of the
steep rocky outcrop to the west of the main pyr-
amid (Fig. 9). Cut by a modern canal, ancient
floors and fills were exposed, and these were

reminiscent of features such as circular courts
such as those found at Cardal. However, clear-
ing and excavation in this area revealed that the
remains actually corresponded to another mas-
sive wall running for at least 105 m, with a
width of 5 m and a height of 5 m. The stone-
work and construction were similar to those al-
ready described, and there was evidence of two
episodes of renovation in which additional
walls were added. In the 1 998 excavations of a
small section of this wall, late Initial Period pot-
tery was recovered from intact floor surfaces
along the wall's eastern face. This evidence,
combined with the construction style and tech-
nique, lends support to the conclusion that this
and the other monumental walls at Manchay

100

R. L. Burger

Figure 7. Rocky outcrop immediately to the west of the Manchay Banjo complex. Traces of the monumental
wall at the foot of the outcrop were visible prior to excavation and can be seen near the stadia rod in this 1998
photograph. (Photograph by Richard L. Burger.)

El Nino, Early Peruvian Civilization, and Human Agency

101

Figure 8. Excavation in 1999 of the eastern face of the monumental wall at Manchay Bajo. (Photograph by
Richard L. Burger.)

Bajo are coeval with the platform complex and
were built by the same population. It is hypoth-
esized that this wall was built to protect the area
of the central mound from debris slides coming
from the steep slopes of the rocky outcrop
above it. Thus, the total extent of the monu-
mental perimetric wall at Manchay Bajo must
include this feature as well, bringing the total
length of the wall constructions to some 850 m.
If a rough calculation is made of the volume of
earth and stone moved to construct these walls,
it produces a figure in excess of 30,000 m 3 .

In 1999, during the second field season, ar-
chaeological excavations were carried out in a
small section of the monumental wall (Sector
VIIA, Excavation 3) in order to clarify its date,
construction history, and the building tech-
niques utilized. The work in this sector was su-
pervised by Marcelo Saco (PUC), and technical
assistance in the interpretation of the stratigra-
phy was provided by the Polish sedimentolo-
gist, Krzyzstof Mastalerz. The excavated units
were located along the wall's north-south sec-
tion, which crosses the mouth of the small lat-
eral quebrada to the west of the site. Initially,

7 m of the eastern face of the wall was cleared
(see Fig. 8). This revealed that the southern half
of this section was well-preserved, while the
northern half had collapsed after the site's aban-
donment. Subsequent excavations in the area
focused on the intact portion of the wall; the
zone investigated had an area of 49 m 2 . This
included a 1-m-wide trench perpendicular to the
wall face. At the conclusion of this excavation,
a 17-m east- west transect of the monumental
wall complemented the horizontal exposure of
the wall's eastern face (Fig. 10).

Judging from the excavations, the original
monumental wall in this area was trapezoidal in
cross-section. The hearting of the wall consists
of loose soil, gravel, and stones. The wall was
built on a sloping surface created by ephemeral
sheet flows that predated the occupation of the
site. Both faces of the wall consisted of roughly
quarried medium-size stones (e.g., 40 X 38 cm)
set in mud mortar. Both sides of the wall cant
inward for greater stability, and as a result, the
upper section of the wall is approximately 2 m
in width and nearly 3 m wide at its base. The
upper section of the original wall was missing.

102

R. L. Burger

Figure 9. The clearing of the masonry visible at the foot of the western rocky outcrop revealed the eastern face
of a monumental wall in association with Initial Period ceramics. Loose rock can be seen on the steep slopes above
the wall. (Photograph by Richard L. Burger.)

El Nino, Early Peruvian Civilization, and Human Agency

103

Figure 10. A trench transecting the monumental wall revealed the western face of the original monumental wall
and evidence for two subsequent enlargements. The trowel rests upon a caliche-like layer formed as the result of
floor deposits pooling up against the western face of the enlarged wall; this layer is absent on the interior or eastern
side of the wall. (Photograph by Richard L. Burger.)

104

R. L. Burger

It was feasible to reach the wall base on the
western face, and it can be demonstrated that
the original wall was over 2 m in height.

Later in the history of Manchay Bajo, the
wall was widened by stone retaining walls built
parallel to the faces of the original wall. Along
the eastern face the new retaining wall was ter-
raced. The lower terrace was 1 m in height, and
1.2 m remains of the upper terrace wall. Along
the western face, sterile fills of gravel and stone
were added, completely burying the original
wall. The massive layers piled against the wall's
original western face were studied in terms of
their sorting and position, to determine whether
they were man-made construction fills or the
result of slumps or debris flows from the lateral
quebrada. These layers include loose, frag-
mented material ranging from angular boulders
to muddy, coarse-grained sand. Sedimentologist
K. Mastalerz (1999) concluded that they were
man-made deposits piled against the western
side of the original wall. These fills added at
least 1 m in height and 4 m in width to the
monumental wall, bringing the total scale of the
wall in this section to over 9 m in width and
over 3 m in height.

Interestingly, the floor articulating with the
western face of the original wall showed evi-
dence of caliche-like cementation due to the
precipitation of soluble compounds from
groundwater. Mastalerz (1999) believes that
such a layer was probably the result of the pool-
ing of water from El Nino rains against the
monumental wall. Significantly, this cementa-
tion was not encountered along the eastern face
of the wall. Little evidence survived of the new
western face of the expanded monumental wall
due to the narrowness of our trench (1m); only
a limited portion of what remained could be
exposed. However, the base of the wall (Muro
6) and its associated floor was identified. Sur-
prisingly, the wall was made of stone-filled shi-
cra bags covered with mud mortar. This tech-
nique of wall construction was rare at the
U-shaped complexes in the Lurin Valley, but it
had been identified previously at Mina Perdida
(Burger and Salazar- Burger 2002). It was pos-
sible to date the fiber used in the shicra in order
to get an idea of the age of the monumental
wall's renovation. The AMS measurement on
this sample produced a date of 3020 40 B.P.
(calibrated 2<r range of 1389-1129 B.C.). This
result confirms the overall contemporaneity of
the monumental wall with the U-shaped civic-

ceremonial complex and the associated residen-
tial constructions at Manchay Bajo. The date
suggests that the original monumental wall was
built early in the site's history and renovated at
least once during the late Initial Period. Judging
from the section excavated, that renovation may
have involved as much labor as the original
construction itself. Finally, it would appear
from the caliche layer that a minimum of one
major El Nino event occurred after the wall was
constructed and while the site was still occu-
pied. It is reasonable to hypothesize that this El
Nino event may have stimulated the enlarge-
ment of the original wall, since the addition
covers the cementation.

There are two other massive layers of gravel
and stone that post-date Muro 6. According to
Mastalerz, these, like the strata they cover, also
are man-made deposits still in their original po-
sition. A possible explanation of these strata is
that they represent a subsequent second phase
of enlargement after the collapse or dismantle-
ment of the shicra wall (Muro 6). This enlarge-
ment to the west could have involved a retain-
ing wall whose traces have disappeared com-
pletely, or, alternatively, as Mastalerz (1999)
suggests, the final outer western surface of the
monumental wall could have been left as an
unfaced embankment. At the end of this hypo-
thetical third construction phase, the monumen-
tal wall would have reached 12 m in width and
increased in height by at least another 50 cm to
3.5 m. We have no way of directly dating this
third episode of wall construction; we suspect
that it could date to the final Early Horizon oc-
cupation of the public center.

The location of the walls, their massive
width, and their substantial height all suggest
that they were built as a dam to protect the civ-
ic-ceremonial complex from land and rock
slides coming off the rocky outcrops and out of
the dry quebradas. It is significant that walls do
not exist to the east or south of the Manchay
Bajo complex, where there is no danger of such
disasters. Moreover, there is evidence that the
walls served their intended purpose with some
success. In all four of the transects that we doc-
umented in 1998, the surface level outside the
wall (i.e., the exterior facing the potential
source of debris) was significantly higher than
inside the wall (i.e., the interior facing the plaza
or platform mounds). It appears that in some
areas, 1-2 m of material had accumulated
against the wall, presumably from one or more

El Nino, Early Peruvian Civilization, and Human Agency

105

debris flows provoked by El Ninos. In one deep
cut to the north of the wall made by modern
builders, this pattern of debris flow evidently
recurred on several occasions both before and
after the wall's construction. Judging from our
excavations within the wall's perimeter, Man-
chay Bajo's monumental wall or dam stopped
the entry of stone rubble from debris flows, as
was intended. In no area inside the wall did we
encounter deposits of boulders or large stones
carried by landslides or other disasters. The
dam also appears to have protected the civic-
ceremonial center from floods during the Initial
Period and Early Horizon occupation of the
site.

Nevertheless, the problem posed by large
quantities of flood water blocked by the mon-
umental wall appears to have presented a seri-
ous problem. Our investigations revealed that
deep layers of water-borne deposits cover most
of the site, with the exception of the elevated
public architecture. For example, an excavation
in the Manchay Bajo's open plaza area (Sector
IV, Excavation 1) revealed that the central sec-
tion of this space featured a low, stone-filled
platform at least 1 m in height. This Initial Pe-
riod construction was buried by over 2 m in
flood deposits, which, according to Mastalerz
(1999), were the product of six El Nino epi-
sodes whose character varied in size and dura-
tion. Some layers of sediments were the result
of flash floods, while others were produced by
powerful floods followed by stagnant water
conditions. In one period the rains were suffi-
cient to stimulate in-channel fluvial processes
and the resulting deposition of sand and gravel
bars at Manchay Bajo. The repeated floods doc-
umented by these deposits came primarily from
the Quebrada Manchay, and it would appear
that the northern section of the dam was
breached on numerous occasions during the last
2000 years following the center's abandonment.
Considerable numbers of Initial Period artifacts
are mixed in with some of these flood deposits,
and it is clear that these floods destroyed some
of the upper layers of the site's Formative set-
tlement. While there is compelling evidence of
destructive floods following Manchay Bajo's
abandonment, at the present time there is no
evidence that floods disrupted the Initial Period
or Early Horizon occupation of the civic-cere-
monial center of Manchay Bajo.

Agents and Environment

The evidence summarized here suggests that ( 1 )
the people of Manchay Bajo perceived a threat
to their center and adjacent agricultural lands
from El Nino-related landslides; (2) they were
able to generate a solution to the problem using
available technology and materials; (3) they
were able to mobilize enough labor to complete
a dam large enough to protect them from El
Nino debris slides; and (4) during some six cen-
turies of occupation, they were able to bring
together enough manpower to renovate the dam
on at least two occasions by encasing the orig-
inal wall within new fills and retaining walls.
The monumental walls succeeded as bulwarks
against the feared landslides, and they are still
capable of doing so. These findings highlight
the importance of human agency in shaping a
culture's destiny; clearly, the actions discussed
here were preemptive, anticipating potential
threats from unpredictable future El Nino
events. The population employed a knowledge
of environmental risks to formulate a strategy,
and they were able to implement this strategy
even though it involved thousands of person-
days of labor without immediate short-term
benefit.

The case of Manchay Bajo provides a good
opportunity to reconsider some of our precon-
ceptions about the ability of different kinds of
societies to cope with environmental variability.
It has often been assumed that states are
uniquely well suited to deal with disasters be-
cause of their coercive capacity, managerial ap-
paratus, and ability to marshal resources from
a wide area. Nevertheless, the continuity and
duration of the Manchay culture for a millen-
nium are a clear demonstration of the resilience
and flexibility of its social forms in the face of
mega-El Ninos and other disasters that must
have occurred. In this respect, the Manchay cul-
ture's lack of centralization and hierarchy may
have been an asset rather than an obstacle. The
mobilization of labor for efforts like the mon-
umental wall should not surprise us, since even
greater projects were undertaken during the sec-
ond millennium to obtain water through gravity
canals. In fact, the creation of new canals was
intimately linked to the establishment of the ag-
ricultural lands needed to support newly estab-
lished social units and their public centers. Oth-
er corporate labor efforts were undertaken to

106

R. L. Burger

obtain supernatural favor through temple con-
struction.

The ability of the Manchay culture's subsis-
tence economy to withstand short-term climatic
disruptions is comprehensible, since its contin-
ued dependence on a range of maritime resourc-
es, hunting, and wild plants would have served
the people well during an El Nino event. More-
over, the social institutions underlying the im-
pressive public constructions of the Manchay
culture would have been an asset in times of
crisis. In times of emergency, the annual mo-
bilization of public labor usually used to refur-
bish the U-shaped pyramid complexes could
have been turned to repairing the relatively
short canals that irrigated their fields and that
would have been damaged by major El Nino
events, or to renovate the monumental dam pro-
tecting the site.

As already noted, the construction technique,
the masonry style, and the pattern of episodic
renovations of the dam differ little from that
used in the temple. In many respects, the chal-
lenge of building a long linear feature like the
Manchay Bajo dam is analogous to the con-
struction of a gravity canal. Contemporary
communities construct and maintain canals
without state intervention by dividing the re-
quired labor between the family units or com-
munities that benefit from the irrigation water,
with participation in the cooperative labor effort
a prerequisite for continued community mem-
bership (i.e., access to land and water). Such
cooperative labor practices have been docu-
mented for pre-Hispanic times, and may have
been in place by the Initial Period (Burger
1992; Mosely 1992). Considering these factors,
it is worth considering whether the pre-state so-
cieties of the Initial Period may have been as
well as or, perhaps, even better equipped to deal
with mega-El Niflos than the more fragile com-
plex societies of later times.

Acknowledgments. Research was conducted
by permission of Peru's Institute Nacional de
Cultura and made possible by grants from the
Heinz Family Foundation, FERCO (the Foun-
dation for Exploration and Research on Cultural
Origins), and The Curtiss T. Brennan and Mary
G. Brennan Foundation. I am deeply grateful to
Lucy C. Salazar, Co-Director of the Proyecto
Lurin, and to archaeologists Jose Pinilla, Ber-
nadino Ojeda, and Marcel Savo, who helped to
supervise the fieldwork. I am also indebted to

Krzysztof Mastalerz for his insights into the
sediments and depositional processes at Man-
chay Bajo.

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A Selected Listing of Other Andean Titles Available

Useful Plants of the Siona and Secoya Indians of Eastern Ecuador. By William T. Vickers and Timothy
Plowman. Fieldiana: Botany, n.s., no. 15, 1984. 63 pages, 24 illus.

Publication 1356, $15.00

The Ethnobotany of Chinchero, an Andean Community in Southern Peru. By Christine Franquemont et
al. Fieldiana: Botany, n.s., no. 24, 1990. 126 pages, 34 illus., erratum.

Publication 1408, $25.00

Archaeological Research at Tumatumani, Juli, Peru. By Charles Stanish et al. Fieldiana: Anthropology,
n.s., no. 23, 1993. Ill pages, 176 illus.

Publication 1457, $23.00

A Revision of the South American Species of Brunfelsia (Solanaceae). By Timothy Plowman. Edited
posthumously by S. Knapp and J. R. Press. Fieldiana: Botany, n.s., no. 39, 1998. 135 pages, 46 illus.
-i- 2 frontispieces (incl. a cool photograph of Tim).

Publication 1496, $40.00

The Early Ceramics of the Inca Heartland. By Brian S. Bauer. Fieldiana: Anthropology, n.s., no. 31,
1999. 156 pages, 105 illus., 4 maps.

Publication 1501, $60.00

An Osteological Study of Nasca Trophy Heads Collected by A. L. Kroeber During the Marshall Field
Expeditions to Peru. By Sloan R. Williams et al. Fieldiana: Anthropology, n.s., no. 33, 2001. 132
pages, 84 illus.

Publication 1516, $30.00

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Full text of "El Niño in Peru : biology and culture over 10,000 years : Papers from the VIII Annual A. Watson Armour III Spring Symposium, May 28-29, 1999, Chicago"

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